Adaptive vehicle control system with driving style recognition based on maneuvers at highway on/off ramps

ABSTRACT

An adaptive vehicle control system that classifies a drivers driving style based on highway on/off ramp maneuvers. Once the maneuver has been determined to be an on-ramp maneuver or an off-ramp maneuver, a style characterization processor can classify the maneuver using selected discriminant features obtained or derived from the maneuver.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates generally to an adaptive vehicle control systemthat includes driving style recognition and, more particularly, to anadaptive vehicle control system that provides driver assistance byidentifying a driver's driving style in terms of driving sportinessbased on highway on/off ramp maneuvers.

2. Discussion of the Related Art

Driver assistance systems and vehicle active safety systems are becomingan integral part of vehicle design and development in an attempt toreduce driving stress and to enhance vehicle/roadway safety. Forexample, adaptive cruise control (ACC) systems are known that relievedrivers from routine longitudinal vehicle control by keeping the vehiclea safe distance away from a preceding vehicle. Also, lane changingdeparture warning systems are know that alert the vehicle driverwhenever the vehicle tends to depart from the traveling lane.

These systems employ various sensors and detectors that monitor vehicleparameters, and controllers that control vehicle systems, such as activefront and rear wheel steering and differential braking. Although suchsystems have the potential to enhance driver comfort and safety, theirsuccess depends not only on their reliability, but also on driveracceptance. For example, considering an ACC system, studies have shownthat although shortening headway distances between vehicles can increasetraffic flow, it can also cause stress to some drivers because of theproximity to a preceding vehicle. Therefore, it may be desirable toenhance such systems by adapting the vehicle control in response to adriver's driving style to meet the needs of different drivers.

SUMMARY OF THE INVENTION

In accordance with the teachings of the present invention, an adaptivevehicle control system is disclosed that classifies a driver's drivingstyle based on maneuvers at highway on/off ramps and road and trafficconditions. The system includes a plurality of vehicle sensors thatdetect various vehicle parameters. A maneuver identification processorreceives the sensor signals to identify a characteristic maneuver of thevehicle and provides a maneuver identifier signal of the maneuver. Thesystem also includes a traffic and road condition recognition processorthat receives the sensor signals, and provides traffic condition signalsidentifying traffic conditions and road condition signals identifyingroad conditions. In one non-limiting embodiment, the road conditionsignals identify road type, such as rural or urban, road surfacecondition, such as moderate or rough, and ambient conditions, such aslight level, rain or snow, and fog. The system also includes a dataselection processor that receives the sensor signals, the maneuveridentifier signals and the traffic and road condition signals, andstores data for each of the characteristic maneuvers and the traffic androad conditions. A style characterization processor receives themaneuver identifier signals, the stored data from the data selectionprocessor and the traffic and road condition signals, and classifiesdriving style based on the signals to classify the style of the driverdriving the vehicle.

In one embodiment, the maneuver identification processor identifies anon-ramp maneuver or an off-ramp maneuver. The process reads the sensorsignals for vehicle speed and vehicle yaw rate from vehicle sensors. Theprocess determines whether the vehicle is turning by determining whetherthe vehicle yaw rate is greater than a first yaw rate threshold and, ifso, determines that the vehicle most likely entered a curve that mightbe the curve portion of a highway on/off ramp. The process determineswhether the vehicle has exited the curve by determining whether thevehicle yaw rate is less than a second yaw rate threshold. The processdetermines whether the difference between vehicle speed at the beginningof the curve and at the end of the curve is less than a first vehiclespeed threshold and, if so, determines that the maneuver is an off-rampmaneuver. The process also determines whether the increase in vehiclespeed during a predetermined time window becomes less than a secondspeed threshold. The process also determines whether the vehicle speedduring a predetermined time window of the maneuver is greater than athird speed threshold. The process also determines whether a differenceof the vehicle speed during the time window minus the speed at the starttime is greater than a fourth speed threshold. The process alsodetermines if the maneuver is an on-ramp maneuver if the increase of thevehicle speed becomes less than a second speed threshold and the speedof the vehicle during the predetermined time window is greater than thethird speed threshold and the difference in the vehicle speed during thetime window minus the speed of the vehicle at the start time is greaterthan the fourth speed threshold. Once the maneuver has been determinedto be an on-ramp maneuver or an off-ramp maneuver, the stylecharacterization processor can classify the maneuver using selecteddiscriminant features extracted from the maneuver.

Additional features of the present invention will become apparent fromthe following description and appended claims, taken in conjunction withthe accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a plan view of a vehicle employing various vehicle sensors,cameras and communications systems;

FIG. 2 is a block diagram of a system providing in-vehiclecharacterization of driving style, according to an embodiment of thepresent invention;

FIG. 3 is a block diagram of a system providing in-vehiclecharacterization of driving style, according to another embodiment ofthe present invention;

FIG. 4 is a block diagram of a system providing in-vehiclecharacterization of driving style, according to another embodiment ofthe present invention;

FIG. 5 is a flow chart diagram showing a process for determining asteering-engaged maneuver in the maneuver identification processor shownin the systems of FIGS. 2, 3 and 4, according to an embodiment of thepresent invention;

FIG. 6 is a block diagram of a system for integrating road conditionsignals in the traffic/road condition recognition processor in thesystems shown in FIGS. 2, 3 and 4, according to an embodiment of thepresent invention;

FIG. 7 is a flow chart diagram showing a processor for identifyingroadway type for use in the traffic/road condition recognition processorin the systems of FIGS. 2, 3 and 4, according to an embodiment of thepresent invention;

FIG. 8 is a flow chart diagram showing a process for providing dataselection in the data selection processor in the systems shown in FIGS.2, 3 and 4, according to an embodiment of the present invention;

FIG. 9 is a flow chart diagram showing a process for providing styleclassification in the style characterization processor of the systemsshown in FIGS. 2, 3 and 4, according to an embodiment of the presentinvention;

FIG. 10 is a block diagram of a style characterization processor thatcan be used in the systems shown in FIGS. 2, 3 and 4, according to anembodiment of the present invention;

FIG. 11 is a block diagram of a style classification processor that canbe used in the systems shown in FIGS. 2, 3 and 4, according to anotherembodiment of the present invention;

FIG. 12 is a block diagram of a style classification processor that canbe used in the systems shown in FIGS. 2, 3 and 4, according to anotherembodiment of the present invention;

FIG. 13 is a block diagram of a style classification processor that canbe used in the systems shown in FIGS. 2, 3 and 4, according to anotherembodiment of the present invention;

FIG. 14 is a block diagram of a process maneuver model system that canbe employed in the style characterization processor of the systems shownin FIGS. 2, 3 and 4 for providing headway control, according to anembodiment of the present invention;

FIG. 15 is a block diagram of the driving style diagnosis processorshown in the system of FIG. 14, according to an embodiment of thepresent invention;

FIG. 16 is a graph with frequency on the horizontal axis and magnitudeon the vertical axis illustrating behavioral differences of variousdrivers;

FIG. 17 is a flow chart diagram showing a process that can be used bythe maneuver identification processor in the systems of FIGS. 2, 3 and 4for detecting a lane-changing maneuver, according to an embodiment ofthe present invention;

FIG. 18 is a flow chart diagram showing a process that can be used bythe maneuver identification processor in the systems of FIGS. 2, 3 and 4for identifying a left/right turn maneuver, according to an embodimentof the present invention;

FIG. 19 is a diagram of a classification decision tree that can be usedby the style characterization processor in the systems of FIGS. 2, 3 and4, according to an embodiment of the present invention;

FIG. 20 is a flow chart diagram showing a process that can be used bythe maneuver identification processor in the systems of FIGS. 2, 3 and 4for identifying a passing maneuver, according to an embodiment of thepresent invention;

FIGS. 21A and 21B are a flow chart diagram showing a process that can beused by the maneuver identification processor in the system of FIGS. 2,3 and 4 for identifying a highway on/off ramp maneuver, according to anembodiment of the present invention;

FIG. 22 is a flow chart diagram showing a process that can be used bythe maneuver identification processor in the systems of figure 2, 3 and4 for identifying a vehicle launching maneuver, according to anembodiment of the present invention;

FIG. 23 is a flow chart diagram showing a process for providing dataselection in the data selection processor in the systems shown in FIGS.2, 3 and 4, according to an embodiment of the present invention;

FIG. 24 is a plan view of a neural network that can be used in the stylecharacterization processor of the systems shown in FIGS. 2, 3 and 4,according to an embodiment of the present invention;

FIG. 25 is a block diagram of a style characterization processor thatcan be used in the systems of FIGS. 2, 3 and 4 that includes a level-1combination, according to an embodiment of the present invention; and

FIG. 26 is a block diagram of a decision fusion processor that can beused in the systems of FIGS. 2, 3 and 4, according to another embodimentof the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

The following discussion of the embodiments of the invention directed toan adaptive vehicle control system that considers a drivers drivingstyle in terms of driving sportiness based on highway on/off rampmaneuvers is merely exemplary in nature, and is in no way intended tolimit the invention or its applications or uses.

The present invention provides various embodiments for an adaptivevehicle control system that adapts to one or both of driving environmentand the driver's driving characteristics. Typical adaptive controlsystems consist of control adaptation algorithms. The present inventionaddresses driving style environment and a driver's drivingcharacteristics to recognize a driver's driving style based on his/herdriving behavior, as well as vehicle control adaptation to therecognized driving style to provide the most desirable vehicleperformance to the driver. In order to provide a vehicle driver with themost desirable performance tailored to a specific drivingcharacteristic, vehicle control adaptation can be realized in variousways. For example, these techniques include using differential brakingor rear wheel steering to augment vehicle dynamic response duringvarious vehicle maneuvers. In the present invention, the controladaptation of an active front steering (AFS) variable gear ratio (VGR)system can be used.

In one non-limiting embodiment, the invention provides an adaptivecontrol system for VGR steering, where the vehicle steering ratio variesnot only with vehicle speed, but also with driving conditions astypically indicated by the vehicle hand-wheel angle. Further, thecontrol adaptation takes into account the driver's driving style orcharacteristics. The resulting adaptive VGR provides tailored vehicleperformance to suit a wide range of driving conditions and driver'sdriving characteristics.

To enable control adaptation for driving characteristics, the presentinvention provides an innovative process that recognizes a driver'sdriving characteristics based on his/her driving behavior. Inparticular, the present invention shows how driving style can becharacterized based on the driver's control input and vehicle motionduring various vehicle maneuvers. The driving style recognition providesan assessment of a driver's driving style, especially the level ofsportiness/assertiveness of the driver, which can be incorporated invarious vehicle control and driver assistance systems, including theadaptive AFS VGR system.

The steering gear ratio of a vehicle represents a proportional factorbetween the steering wheel angle and the road wheel angle. Conventionalsteering systems have a fixed steering gear ratio where the steeringwheel ratio remains substantially constant except for minor variationsdue to vehicle suspension geometry. To improve vehicle handling, VGRsteering systems have been developed. With a VGR steering system, thegear ratio varies with vehicle speed so that the number of steeringwheel turns is reduced at low speeds and the high-speed steeringsensitivity is suppressed. However, current AFS VGR systems mainly focuson on-center handling where the steering wheel angle is relatively smalland the tires are in their linear region. Moreover, the design is acompromise to meet the needs of all types of drivers with one singlespeed/VGR curve. Nevertheless, many drivers, especially sporty typedrivers, expect electric aids to enhance their driving experience evenin situations that an average driver would never encounter.

The AFS VGR adaptive control system of the invention includes anenhanced VGR that alters the steering ratio according to vehicle speedand the steering angle to suit different driving conditions, and anadaptive VGR that adjusts the steering ratio based on a driverspreference/style and skill level.

As mentioned above, known VGR systems alter the steering ratio based onvehicle speed only. However, the corresponding steady-state vehicle yawrate gain is mainly for on-center handling where the vehicle tires areoperating in their linear region. When the hand-wheel angle getsrelatively large, the steady-state rate gain drops due to tirenon-linearity.

To compensate for the effects of tire non-linearity and to provide anapproximately uniform yaw rate gain at each vehicle speed, the presentinvention proposes an enhanced VGR that is extended to be a function ofboth vehicle speed v and the vehicle hand-wheel angle δ_(HWA). Theenhanced VGR has the same value as a conventional VGR if the hand-wheelangle δ_(HWA) is smaller than a threshold δ_(th), and decreases as thehand-wheel angle δ_(HWA) increases beyond the threshold δ_(th). Thethreshold δ_(th) is the critical steering angle and steering angleslarger than the threshold δ_(th) result in vehicle tires operating intheir non-linear region.

To accommodate the various needs of different drivers, the adaptive VGRsystem of the present invention incorporates driving style and skilllevels, together with the vehicle speed v and the hand-wheel angleδ_(HWA), to determine the variable gear ratio. The adaptive VGRr_(adaptive) can be calculated by:r _(adaptive) =f _(adaptive)(v,δ _(HWA) ,P,S)  (1)Where P represents driving style, such as P=1-5 where 1 represents aconservative driver and 5 represents a very sporty driver, and Srepresents driving skill level, such as S=1-5 where 1 represents a lowskill driver and 5 represents a high skill driver.

The adaptive VGR r_(adaptive) can be further derived from the enhancedVGR as:

$\begin{matrix}\begin{matrix}{r_{adaptive} = {f_{adaptive}( {v,\delta_{HWA},P,S} )}} \\{= {{k( {v,\delta_{HWA},P,S} )} \times {f_{enhanced}( {v,\delta_{HWA}} )}}}\end{matrix} & (2)\end{matrix}$Where k(v, δ_(HWA), P, S) is a scaling factor.

The vehicle speed v and the hand-wheel angle δ_(HWA) can be measured byin-vehicle sensors, such as wheel speed sensors and a steering anglesensor. Driving style and skill level can be set by the driver orcharacterized by algorithms based on vehicle sensor information.

Because sporty drivers typically prefer the vehicle to be moreresponsive, a lower gear ratio is preferred to yield a higher yaw rategain. On the other hand, drivers need to have the capability to controlthe vehicle as it becomes more sensitive with a lower gear ratio,especially at higher speeds. In other words, a low gear ratio at higherspeeds will only be available to skillful drivers. Therefore, thescaling factor k is smaller for drivers with a higher skill level.

In order to facilitate control adaptation based on driving style, thepresent invention further proposes a method and system for achieving anin-vehicle characterization of a driver's driving style. Thecharacterization result can be used in various vehicle controlalgorithms that adapt to a driver's driving style. However, such controlalgorithms are neither prerequisites nor components for the in-vehiclecharacterization system of the invention.

FIG. 1 is a plan view of a vehicle 10 including various sensors, visionsystems, controllers, communications systems, etc., one or more of whichmay be applicable for the adaptive vehicle control systems discussedbelow. The vehicle 10 includes mid-range sensors 12, 14 and 16 at theback, front and sides, respectively, of the vehicle 10. A front visionsystem 20, such as a camera, provides images towards the front of thevehicle 10 and a rear vision system 22, such as a camera, providesimages towards the rear of the vehicle 10. A GPS or a differential GPSsystem 24 provides GPS coordinates, and a vehicle-to-infrastructure(V2X) communications system 26 provides communications between thevehicle 10 and other structures, such as other vehicles, road-sidesystems, etc., as is well understood to those skilled in the art. Thevehicle 10 also includes an enhanced digital map (EDMAP) 28 and anintegration controller 30 that provides surround sensing data fusion.

FIG. 2 is a block diagram of an adaptive control system 40 that providesin-vehicle characterization of a driver's driving style, according to anembodiment of the present invention. The system 40 has application forcharacterizing a driver's driving style based on various types ofcharacteristic maneuvers, such as curve-handling maneuvers, vehiclelaunching maneuvers, left/right turns, U-turns, highway on/off-rampmaneuvers, lane changes, etc.

The system 40 employs various known vehicle sensors identified as anin-vehicle sensor suite 42. The sensor suite 42 is intended to includeone or more of a hand-wheel angle sensor, a yaw rate sensor, a vehiclespeed sensor, wheel speed sensors, longitudinal accelerometer, lateralaccelerometer, headway distance sensors, such as a forward-lookingradar-lidar or a camera, a throttle opening sensor, a brake pedalposition/force sensor, etc., all of which are well known to thoseskilled in the art. The sensor signals from the sensor suite 42 areprovided to a signal processor 44 that processes the sensor measurementsto reduce sensor noise and sensor biases. Various types of signalprocessing can be used by the processor 44, many of which are well knownto those skilled in the art.

The processed sensor signals from the signal processor 44 are providedto a maneuver identification processor 46, a data selection processor 48and a traffic/road condition recognition processor 50. The maneuveridentification processor 46 identifies various types of characteristicmaneuvers performed by the driver. Such characteristic maneuversinclude, but are not limited to, vehicle headway control, vehiclelaunching, highway on/off-ramp maneuvers, steering-engaged maneuvers,which may be further separated into curve-handling maneuvers, lanechanges, left/right turns and U-turns. Details of using those types ofcharacteristic maneuvers for style characterization will be discussedbelow. Maneuver identification is provided because specificmethodologies used in style characterization may differ from one type ofcharacteristic maneuver to another. For example, characterization basedon headway control behaviors during vehicle following use headwaydistance and closing speed from a forward-looking radar, whilecharacterization based on curve-handling maneuvers involves yaw rate andlateral acceleration. Therefore, the type of maneuvers conducted by thedriver need to be identified. When the maneuver identification processor46 identifies a particular type of maneuver of the vehicle 10, it willoutput a corresponding identification value to the data selectionprocessor 48.

Not all maneuvers can be easily identified from in-vehicle motion sensormeasurements. Further, some maneuvers reveal driving style better thanothers. Such maneuvers that help distinguish driving style are referredto as characteristic maneuvers. Consequently, only data corresponding tocharacteristic maneuvers is selected and stored for the stylecharacterization. The maneuver identification processor 16 identifiescharacteristic maneuvers based on any combination of in-vehicle sensors,such as a vehicle speed sensor, a longitudinal acceleration sensor, asteering wheel angle sensor, a steering angle sensor at the wheels, ayaw rate sensor, a lateral acceleration sensor, a brake pedal positionsensor, a brake pedal force sensor, an acceleration pedal positionsensor, an acceleration pedal force sensor, a throttle opening sensor, asuspension travel sensor, a roll rate sensor, a pitch rate sensor, aswell as long-range and short-range radars, cameras, GPS or DGPS mapinformation, and vehicle-to-infrastructure/vehicle communication. Themaneuver identification processor 16 may further utilize any combinationof information processed from the measurements from those sensors,including the derivatives and integrated signals. Once the maneuveridentification processor 16 detects a characteristic maneuver, itinforms the data selection processor 48 to start recording data. Themaneuver identification processor 16 also identifies the end of themaneuver so that the data selection processor 48 stops recording. Thetraffic information from the recognition processor 50 may also beincorporated in the recording process to determine whether the maneuvercontains adequate information for style characterization.

The traffic/road condition recognition processor 50 uses the sensorsignals to recognize traffic and road conditions. Traffic conditions canbe evaluated based on traffic density. Roadway conditions include atleast two types of conditions, specifically, roadway type, such asfreeway/highway, city streets, winding roads, etc., and ambientconditions, such as dry/wet road surfaces, foggy, rainy, etc. Systemsthat recognize road conditions based on sensor input are well known tothose skilled in the art, and need not be described in detail herein.

The style characterization processor 52 receives information of acharacteristic maneuver from the maneuver identification processor 46,the traffic and road condition information from the traffic/roadcondition recognition processor 50 and the recorded data from the dataselection processor 48, and classifies driving style based on theinformation. As the maneuver identifier processor 46 determines thebeginning and the end of a maneuver, the data selection processor 48stores the corresponding data segment based on the variables Start_flag,End_flag, t_(start) and t_(end).

The output from the style characterization processor 52 is a value thatidentifies a driving style over a range of values, such as a one for aconservative driving up to a five for sporty driving. The particularstyle characterization value is stored in a style profile trip-logger 54for each particular characteristic maneuver identified by theidentification processor 46. The trip-logger 54 can be a simple dataarray where each entry array contains a time index, the maneuverinformation, such as maneuver identifier M_(i)d, traffic/road conditioninformation, such as traffic index and road index, and the correspondingcharacterization result. To enhance the accuracy and robustness of thecharacterization, a decision fusion processor 56 integrates recentresults with previous results stored in the trip-logger 54.

FIG. 3 is a block diagram of an adaptive control system 60 that providesin-vehicle characterization of driving style, according to anotherembodiment of the present invention, where like elements to the system40 are identified by the same reference numeral. In the system 60, avehicle positioning processor 62 is included that receives the processedsensor measurement signals from the signal processor 44. In addition,the system 60 includes a global positioning system (GPS) or differentialGPS 64, such as the GPS 24, and an enhanced digital map 66, such as theEDMAP 28. Information from the vehicle positioning processor 62 isprovided to the traffic/road condition recognition processor 50 toprovide vehicle location information. Additionally, the system 60includes a surround sensing unit 68, which comprises long-range andshort-range radars/lidars at the front of the vehicle 10, short-rangeradars/lidars on the sides and/or at the back of the vehicle 10, orcameras around the vehicle 10, and a vehicle-to-vehicle/infrastructurecommunication system 70 that also provides information to thetraffic/road condition recognition processor 50 for additionalinformation concerning traffic and road conditions.

The vehicle positioning processor 62 processes the GPS/DGPS information,as well as information from vehicle motion sensors, to derive absolutevehicle positions in earth inertial coordinates. Other information, suchas vehicle heading angle and vehicle speed, may also be derived. Thevehicle positioning processor 62 further determines vehicle locationwith regard to the EDMAP 66 and retrieves relevant local road/trafficinformation, such as road curvature, speed limit, number of lanes, etc.Various techniques for GPS/DGPS based positioning and vehicle locatingare well-known to those skilled in the art. Similarly, techniques forsurround sensing fusion and vehicle-to-vehicle/infrastructure (V2X)communications are also well known to those skilled in the art. Thus, byusing this information, the traffic/road condition recognition processor50 has a stronger capability of more accurately recognizing traffic androad conditions.

FIG. 4 is a block diagram of an adaptive control system 80 similar tothe control system 60, where like elements are identified by the samereference numeral, according to another embodiment of the presentinvention. In this embodiment, the system 80 is equipped with a driveridentification unit 82, a style profile database 84 and a trend analysisprocessor 86 to enhance system functionality. The driver identificationunit 82 can identify the driver by any suitable technique, such as bypressing a key fob button. Once the driver is identified, his or herstyle profile during each trip can be stored in the style profiledatabase 84. Further, a history separate style profile can be built upfor each driver over multiple trips, and can be readily retrieved to befused with information collected during the current vehicle trip.Further, a deviation of the style exhibited in the current trip fromthat in the profile history may imply a change in driver state. Forexample, a conservative driver driving aggressively may indicate that heor she is in a hurry or under stress. Similarly, a sporty driver drivingconservatively may indicate that he or she is tired or drowsy.

As mentioned above, various characteristic maneuvers can be used in thestyle characterization, such as vehicle headway control, vehiclelaunching, highway on/off ramp maneuvers, and steering-engagedmaneuvers, which referred to maneuvers that involve a relatively largesteering angle as and/or a relatively large vehicle yaw rate. Thesteering-engaged maneuvers may be further broken down intosub-categories, such as lane changes, left/right turns, U-turns andcurve-handling maneuvers where a vehicle is negotiating a curve. Furtherdiscussions of identifying those specific sub-categories have specialtypes of steering-engaged maneuvers will be included together with thecorresponding illustration.

In one embodiment, the steering-engaged maneuvers are treated as onetype of characteristic maneuver. Accordingly, the reliable indicators ofa steering-engaged maneuver include a relatively large vehicle yaw rateand/or a relatively large steering angle. In one embodiment, the yawrate is used to describe the operation of the maneuver identificationprocessor 46, where a steering-angle based data selector would work in asimilar manner. To maintain the data integrity of the associatedsteering-engaged maneuver, a certain period, such as T=2 s, of databefore and after the steering-engaged maneuver is also desired.

FIG. 5 is a flow chart diagram 280 showing a process that can be used bythe maneuver identification processor 46 to determine steering-engagedmaneuvers. The maneuver identifier value M_(id) is used to identify thetype of the characteristic maneuver, as will be discussed in furtherdetail below. Each of these discussions will use a maneuver identifiervalue M_(id) of 0, 1 or 2 to identify the maneuver. This is merely forillustration purposes in that a system that incorporated maneuverdetection for all of the various maneuvers would use a different valuefor the maneuver identifier value M_(id) for each separate maneuverbased on the type of specific characteristic maneuver.

At box 282, the maneuver identification algorithm begins by reading thefiltered yaw rate signal ω from the signal processor 44. The algorithmthen proceeds according to its operation states denoted by two Booleanvariables Start_flag and End_flag, where Start_flag is initialized tozero and End_flag is initialized to one. At block 284, the algorithmdetermines whether Start_flag is zero.

If Start_flag is zero, meaning that the vehicle 10 is not in asteering-engaged maneuver, the algorithm determines if the vehicle 10has started a steering-engaged maneuver based on the yaw rate signal ωat decision diamond 286 by determining whether ω(t)≧ω_(med), whereω_(med) is 5° per second in one non-limiting embodiment. If thiscondition is met, meaning that the vehicle 10 has started asteering-engaged maneuver, the algorithm sets Start_flag to one andEnd_flag to zero at box 288, and starts a timer t_(start)=t−T at box290. If the condition of the decision diamond 286 has not been met,meaning that the vehicle 10 has not started a steering-engaged maneuver,then the algorithm returns and waits for the next sensor measurement atblock 292.

If Start_flag is not zero at the block 284, meaning that the vehicle 10is in a steering-engaged maneuver, the algorithm determines whether thesteering-engaged maneuver is completed by determining whether the yawrate signal ω has been reduced to near zero at block 294 bymax(ω(t−T:t))≦ω_(small), where ω_(small) is 2° per second in onenon-limiting embodiment. If this condition is not met, meaning that thevehicle 10 is still in the steering-engaged maneuver, the algorithmreturns to the block 292 to collect the next cycle of data. If thecondition of the block 294 has been met, meaning that the vehicle 10 hascompleted the steering-engaged maneuver, the algorithm sets Start_flagto zero, End_flag to one and the timer t_(end)=t−T at box 296. Thealgorithm then sets the maneuver identifier value M_(id) to one at box298 meaning that a steering-engaged maneuver has just occurred, and isready to be classified.

The traffic/road condition recognition processor 50 detects trafficconditions. The traffic conditions can be classified based on trafficdensity, for example, by using a traffic density condition indexTraffic_(index). The higher the index Traffic_(index), the higher thetraffic density. Such a traffic index can also be derived based onmeasurements from sensors, such as radar-lidar, camera and DGPS withinter-vehicle communication.

As an example, the processor 50 can be based on a forward-looking radaras follows. The detection process involves two steps, namely, inferringthe number of lanes and computing the traffic index Traffic_(index).Usually, radar measurements are processed to establish and maintainindividual tracks for moving objects. Such information is stored in abuffer for a short period of time, such as five seconds, the currentroad geometry can be estimated by fitting individual tracks with thepolynomials of the same structure and parameters except their offsets.The estimated offsets can be used to infer the number of lanes, as wellas the relative position of the lane occupied by the subject vehicle.

With the estimate of the number of lanes, the traffic indexTraffic_(index) can be determined as:Traffic_(index) =f(N _(lane) ,N _(track) ,R,v)  (3)Where N_(lane) is the number of lanes, N_(track) is the number ofvehicles being tracked, R is the range to the preceding vehicle and v isthe speed of the subject vehicle.

An alternative and also more objective choice is to use the averagerange between vehicles in the same lane and the average speed on theroad. However, the computation of such variables would be morecomplicated.

An example of the function of equation (3) can be given as:

$\begin{matrix}{{Traffic}_{index} = \{ \begin{matrix}{{{a\;\frac{N_{track}}{N_{lane}}} + {b\;\frac{v}{R}}},} & {N_{track} > 0} \\{0,} & {N_{track} = 0}\end{matrix} } & (4)\end{matrix}$Thus, the larger N_(track)/N_(lane) and v/R, the larger the trafficindex Traffic_(index), i.e., the density of traffic. For the situationwhere there is no preceding or forward vehicle i.e., N_(track) equalszero, the traffic index Traffic_(index) is set to zero.

It is noted that in the cases where there are multiple lanes, but novehicles in the adjacent lanes, the number of lanes will be estimated asone, which is incorrect. However, in such cases, the driver has morefreedom to change lanes instead of following close to the precedingvehicle. Consequently v/R should be small and so should the trafficindex Traffic_(index).

A second embodiment for recognizing traffic conditions in terms oftraffic density is based on DGPS with inter-vehicle communication. Withthe position and motion information of surrounding vehicles frominter-vehicle communication, the subject vehicle can assess the numberof surrounding vehicles within a certain distance, as well as theaverage speed of those vehicles. Further, the subject vehicle candetermine the number of lanes based on the lateral distance betweenitself and its surrounding vehicles. To avoid counting vehicles andlanes for opposing traffic, the moving direction of the surroundingvehicles should be taken into consideration. With this type ofinformation, the traffic index Traffic_(index) can be determined byequation (4).

While the equations (3) and (4) used the vehicles headway distanceR_(hwd) to the preceding vehicle as the range value R, it can be moreaccurate to use a weighted range variable based on the longitudinal gapsbetween vehicles in the same lane as the range variable R whensituations permit. With a side-view sensor to detect a passing vehicle,the relative speed Δv between the passing vehicle and the subjectvehicle can be detected to provide timing ΔT between one vehicle andanother. Therefore, the ith occurrence of the gap R_(gap) betweenvehicles in adjacent lanes can be estimated as:R _(gap)(i)=Δv*ΔT  (5)

The range variable R can be estimated as a weighted average between theheadway distance R_(hwd) and the running average of the adjacent lanevehicle gaps as:

$\begin{matrix}{R = {{aR}_{hwd} + {( {1 - a} )\frac{\overset{N}{\sum\limits_{1}}{R_{gap}(i)}}{N}}}} & (6)\end{matrix}$Where a is a parameter between 0 and 1.

When a rear-looking sensor is available, the trailing vehicle distanceR_(trail) can be measured. This measurement can further be incorporatedfor range calculation, such as:

$\begin{matrix}{R = {{\frac{a}{2}( {R_{hwd} + R_{trail}} )} + {( {1 - a} )\frac{\overset{N}{\sum\limits_{1}}{R_{gap}(i)}}{N}}}} & (7)\end{matrix}$

Traffic density can further be assessed using vehicle-to-vehicle (V2V)communications with the information of GPS location communicated amongthe vehicles. While the vehicle-to-vehicle communications equippedvehicle penetration is not 100%, the average distances between vehiclescan be estimated based on the geographic location provided by the GPSsensor. However, the information obtained through vehicle-to-vehiclecommunications needs to be qualified for further processing. First, amap system can be used to check if the location of the vehicle is alongthe same route as the subject vehicle by comparing the GPS detectedlocation of the object vehicle with the map data base. Second, therelative speed of this vehicle and the subject vehicle is assessed tomake sure the vehicle is not traveling in the opposite lane. Similarinformation of the object vehicle so relayed through multiple stages ofthe vehicle-to-vehicle communications can be analyzed the same way. As aresult, a collection of vehicle distances to each of thevehicle-to-vehicle communications equipped vehicles can be obtained.Average distances D_(V2V) of these vehicles can be computed for anindication of traffic density.

The traffic index Traffic_(index) can further be improved by:Traffic_(index) =pC ₁ D _(V2V) +C ₂Traffic_(index) _(—) _(raw)  (8)Where, traffic_(indexraw) is based on equation (4), p is the percentagepenetration of the vehicle-to-vehicle communications equipped vehiclesin certain locale determined by a database and GPS sensing information,and where C₁ and C₂ are weighting factors.

The traffic index Traffic_(index) can be computed using any of theabove-mentioned approaches. However, it can be further rationalized forits intended purposes by using this index to gauge driver's behavior toassess the driving style in light of the traffic conditions. For thispurpose, the traffic index Traffic_(index) can further be modified basedon its geographic location reflecting the norm of physical trafficdensity as well as the average driving behavior.

Statistics can be established off-line to provide the average un-scaledtraffic indices based on any of the above calculations for the specificlocations. For example, a crowded city as opposed to a metropolitan areaor even a campus and everywhere else in the world. This information canbe stored in an off-sight installation or infrastructure accessiblethrough vehicle-to-infrastructure communications. When such informationis available, the traffic index Traffic_(index) can be normalizedagainst the statistical mean of the specific location, and provide amore accurate assessment of the driving style based on specific behaviorover certain detected maneuvers.

The traffic/road condition recognition processor 50 also recognizes roadconditions. Road conditions of interest include roadway type, roadsurface conditions and ambient conditions. Accordingly, three indexescan be provided to reflect the three aspects of the road conditions,particularly road_(type), road_(surface) and road_(ambient),respectively.

FIG. 6 is a block diagram of a system 300 that can be used to recognizeand integrate these three aspects of the road condition. The system 300includes a road type determination processor 302 that receives sensorinformation from various sensors in the vehicle 10 that are suitable toprovide roadway type. The output of the road type determinationprocessor 302 is the roadway condition index road_(type). The roadwaytypes can be categorized in many different ways. For drivingcharacterization, the interest is in how much freedom the roadwayprovides to a driver. Therefore, it is preferable to categorize roadwaysaccording to their speed limit, the typical throughput of the roadway,the number of lanes in each travel direction, the width of the lanes,etc. For example, the present invention categorizes roadways in fourtypes, namely, urban freeway, urban local, rural freeway and rurallocal. The two freeways have a higher speed than the two local roadways.The urban freeway typically has at least three lanes in each travel ofdirection and the rural freeway typically has one to two lanes in eachdirection. The urban local roadways have wider lanes and more trafficcontrolled intersections than the rural local roadway. Accordingly, theroadway type can be recognized based on the following roadcharacteristics, namely, the speed limit, the number of lanes, the widthof the lanes and the throughput of the road if available.

For systems of this embodiment of the invention, the images from aforward-looking camera can be processed to determine the current speedlimit based on traffic sign recognition, the number of lanes and thelane width. In other embodiments, the vehicles can be equipped with aGPS or DGPS with enhanced digital map or GPS or DGPS withvehicle-to-vehicle infrastructure communications, or both. If an EDMAPis available, the EDMAP directly contains the road characteristicsinformation. The EDMAP may even contain the roadway type, which can beused directly. If vehicle-to-infrastructure communications is available,the vehicle will be able to receive those road characteristics and/orthe roadway type in the communication packets from the infrastructure.

With this information, the processor 302 categorizes the roadway typebased on the road characteristics, or the vehicle may directly use theroadway type from the EDMAP 28 with the communications.

FIG. 7 is a flow chart diagram 320 showing a process to provide roadwaytype recognition in the processor 302, according to one non-limitingembodiment of the present invention. In this example, the roadway typecondition index road_(type) is identified as 1 at box 322, as 2 at box324, as 3 at box 326 and as 4 at box 328, where index 1 is for an urbanfreeway, index 2 is for a rural freeway, index 3 is for an urban localroad and index 4 is for a rural local road. The roadway type recognitionstarts with reading the four characteristics. If the current speed limitis above 55 mph at block 330, the roadway is regarded to be either anurban freeway or a rural freeway. The process then determines whetherthe number of lanes is greater than two at block 332, and if so, theroadway is a road type 1 for an urban freeway at the box 322, otherwisethe roadway is a rural freeway type 2 having more than two lanes at thebox 324. If the speed limit is less than 55 mph at the block 330, thealgorithm determines whether the number of lanes is greater than orequal to 2 at block 334. If the number of lanes is at least two, theroad is considered to be an urban local roadway type 3 at the box 326,otherwise it is a rural local roadway of type 4 at the box 328.

The roadway surface affects the ease of the control of a vehicle. Forexample, a low-coefficient surface has limited capability in providinglongitudinal and lateral tire forces. As a result, a driver needs to bemore careful driving on a low coefficient of friction surface than on ahigh coefficient or friction surface. Similarly, the disturbancegenerated by a rough surface makes the ride less comfortable and puts ahigher demand on the drivers control over the vehicle. Such factorsusually cause a driver to be more conservative. Because both thedetection of the friction coefficients of a road surface and thedetection of rough roads using in-vehicle sensors are well-known tothose skilled in the art, a more detailed discussion is not neededherein.

The present invention uses the detection results to generate the roadsurface condition index road_(surface) to reflect the condition of theroad surface. For example, a road surface condition index road_(surface)of zero represents a good surface that has a high coefficient offriction and is not rough, a road surface condition index road_(surface)of one represents a moderate-condition surface that has a mediumcoefficient of friction and is not rough, and a road surface conditionindex road_(surface) of 2 represents a bad surface that has a lowcoefficient or is rough. Returning to FIG. 6, the system 300 includes aroad surface condition processor 304 that receives the sensorinformation, and determines whether the road surface condition indexroad_(surface) is for a moderate coefficient road surface at box 308 ora rough coefficient at box 310.

The ambient conditions mainly concern factors that affect visibility,such as light condition (day or night), weather condition, such as fog,rain, snow, etc. The system 300 includes an ambient condition processor306 that provides the road ambient condition index road_(ambient). Theambient condition processor 306 includes a light level detection box 312that provides an indication of the light level, a rain/snow detectionbox 314 that provides a signal of the rain/snow condition and a fogdetection box 316 that provides a detection of whether fog is present,all of which are combined to provide the road ambient condition indexroad_(ambient).

The sensing of the light condition by the box 312 can be achieved by atypical twilight sensor that senses light level as seen by a driver forautomatic headlight control. Typically, the light level output is acurrent that is proportional to the ambient light level. Based on thisoutput, the light level can be computed and the light condition can beclassified into several levels, such as 0-2 where zero represents brightdaylight and two represents a very dark condition. For example,light_(level)=0 if the computed light level is higher than the thresholdL_(high), where L_(high)=300 lux, light_(level)=1 if the light level isbetween thresholds L_(high) and L_(low), where L_(low) can be theheadlight activation threshold or 150 lux, and light_(level)=2 if thelight level is lower than the threshold L_(low).

The rain/snow condition can be detected by the box 314 using anautomatic rain sensor that is typically mounted on the inside surface ofthe windshield and is used to support the automatic mode of windshieldwipers. The most common rain sensor transmit an infrared light beam at a45° angle into the windshield from the inside near the lower edge, andif the windshield is wet, less light makes it back to the sensor. Somerain sensors are also capable of sensing the degree of the rain so thatthe wipers can be turned on at the right speed. Therefore, the rain/snowcondition can be directly recognized based on the rain sensor detection.Moreover, the degree of the rain/snow can be determined based by eitherthe rain sensor or the windshield wiper speed. Alternatively, therain/snow condition can be detected solely based on whether thewindshield wiper has been on for a certain period of time, such as 30seconds. The rain/snow condition can be categorized into 1+N levels withrain_(level)=0 representing no rain and rain_(level)=i with i indicatingthe speed level of the windshield wiper since most windshield wipersoperate at discrete speeds. Alternatively, if the vehicle is equippedwith GPS or DGPS and a vehicle-to-infrastructure communication, therain/snow condition can also be determined based on rain/snow warningsbroadcast from the infrastructure.

The fog condition can be detected by the box 316 using a forward-lookingcamera or lidar. The images from the camera can be processed to measurethe visibility distance, such as the meteorological visibility distancedefined by the international commission on illumination as the distancebeyond which a black object of an appropriate dimension is perceivedwith a contrast of less than 5%. A lidar sensor detects fog by sensingthe microphysical and optical properties of the ambient environment.Based on its received fields of view, the lidar sensor is capable ofcomputing the effective radius of the fog droplets in foggy conditionsand calculates the extinction coefficients at visible and infraredwavelengths. The techniques for the fog detection based on a camera orlidar are well-known to those skilled in the art, and therefore need notbe discussed in significant detail herein. This invention takes resultsfrom those systems, such as the visibility distance from a camera-basedfog detector or, equivalently, the extension coefficients at visiblewavelengths from a lidar-based fog detection system, and classifies thefollowing condition accordingly. For example, the foggy condition can beclassified into four levels 0-3 with 0 representing no fog and 3representing a high-density fog. The determination of the fog densitylevel based on the visibility distance can be classified as:

$\begin{matrix}{{fog}_{level} = \{ \begin{matrix}{0,} & {{{if}\mspace{14mu}{visibility}} \geq {visibilty}_{high}} \\{1,} & {{{if}\mspace{14mu}{visibility}_{med}} \leq {visibilty} < {visibilty}_{high}} \\{2,} & {{{if}\mspace{14mu}{visibility}_{low}} \leq {visibilty} < {visibilty}_{med}} \\{3,} & {{{if}\mspace{14mu}{visibilty}} < {visibilty}_{low}}\end{matrix} } & (9)\end{matrix}$Where exemplary values of the thresholds can be visibility_(high)=140 m,visibility_(med)=70 m and visibility_(low)=35 m. Alternatively, if thevehicle 10 is equipped with GPS or DGPS and vehicle-to-infrastructurecommunications, the foggy condition may also be determined based on thefog warnings broadcast from the infrastructure.

The road ambient condition index Road_(ambient) then combines thedetection results of the light condition, the rain/snow condition, andthe foggy condition. The simplest way is to letRoad_(ambient)=[light_(level) rain_(level) fog_(level)]^(T).

Alternatively, the road ambient condition index Road_(ambient) could bea function of the detection results such as:

$\begin{matrix}\begin{matrix}{{Road}_{ambient} = {f_{ambient}( {{light}_{level},{rain}_{level},{fog}_{level}} )}} \\{= {{\alpha_{1} \times {light}_{level}} + {\alpha_{2}{rain}_{level}} + {\alpha_{3} \times {fog}_{level}}}}\end{matrix} & (10)\end{matrix}$Where a₁, a₂, and a₃ are weighting factors that are greater than zero.Note that the larger each individual detection result is, the worse theambient condition is for driving. Consequently, the larger the ambientroad condition index Road_(ambient) the worse the ambient condition isfor driving.

The three road condition indexes, Road_(type), Road_(surface),Road_(ambient), are then combined by the system 300 to reflect the roadcondition. The combination can be a simple combination, such asRoad_(index)=[road_(type) road_(surface) road_(ambient)]^(T), or afunction, such as Road_(index)=f_(road)(road_(type) road_(surface)road_(ambient)), which could be a look-up table.

Thus, recognized traffic/road conditions can be used in the stylecharacterization processor 52 in two ways. First, the data selectionprocessor 48 determines the portion of data to be recorded for styleclassification based on the maneuver identifier value Mid and therecognized traffic/road conditions. Second, the style classificationprocessor 52 classifies driving style based on driver inputs and vehiclemotion, as well as the traffic/road conditions. That is, thetraffic/road condition indexes are part of the discriminant features(discussed below) used in the style classification.

Not all data measured during driving is useful. In fact it would beunnecessary and uneconomic to record all of the data. In the presentinvention, information regarding the maneuver type and the traffic/roadconditions help determine whether the current driving behavior isvaluable for the characterization. If so, the data is recorded by thedata selection processor 48. For example, if the traffic is jammed, itmay be meaningless to characterize the style based on lane-changemaneuvers. In such cases, the data should not be stored. On the otherhand, if the traffic is moderate, the data should be recorded that themaneuver is a characteristic maneuver. To maintain the completeness ofthe recording, a short period of data is always recorded and refreshed.

FIG. 8 is a flow chart diagram 130 showing a process used by the dataselection processor 48 for storing the data corresponding to aparticular characteristic maneuver. This process for the data selectionprocessor 48 can be employed for various characteristic maneuvers,including, but not limited to, a vehicle passing maneuver, aleft/right-turn maneuver, a lane-changing maneuver, a U-turn maneuver,vehicle launching maneuver and an on/off-ramp maneuver, all discussed inmore detail below. At start block 132, the algorithm used by the dataselection processor 48 reads the Boolean variables Start_flag andEnd_flag from the maneuver identifier processor 46. If Start_flag iszero or the traffic index Traffic_(index) is greater than the trafficthreshold δ_(th) at decision diamond 134, the data selection processor48 simply keeps refreshing its data storage to prepare for the nextcharacteristic maneuver at block 136.

If either of the conditions of the decision diamond 134 is not met, thenthe algorithm determines whether a variable old_Start_flag is zero atblock 138. If old_Start_flag is zero at the block 138, the algorithmsets old_Start_flag to one, and starts recording by storing the databetween time t_(start) and the current time t at box 140. The data caninclude vehicle speed, longitudinal acceleration, yaw rate, steeringangle, throttle opening, range, range rate and processed information,such as traffic index and road condition index.

If old_Start_flag is not zero at the block 138, the data selectionprocessor 48 is already in the recording mode, so it then determineswhether the maneuver has been completed. Particularly, the algorithmdetermines whether End_flag is one at block 142 and, if so, the maneuverhas been completed. The algorithm then resets old_Start_flag to zero atbox 144, and determines whether the maneuver identifier value M_(id) iszero at decision diamond 146. If the maneuver value M_(id) is not zeroat the decision diamond 146, then the data selection processor 48outputs the recorded data, including the value M_(id), and increases themaneuver sequence index M_(seq)=M_(seq)+1 at box 148. The data selectionprocessor 48 also stores the data between the time t_(start) and thetime tend together with the values M_(seq) and M_(id), and sets avariable data_ready=1 to inform the style characterization processor 52that the recorded data is ready. The algorithm then begins a new sessionof data recording at box 150.

If End_flag is not one at the block 142, the maneuver has not beencompleted, and the data selection processor 48 continues storing the newdata at box 152.

The collected data is then used to determine the driving style, wherethe Boolean variable data will be used by the style characterizationprocessor 52 to identify a classification process.

According to one embodiment of the present invention, the stylecharacterization processor 52 classifies a driver's driving style basedon discriminant features. Although various classification techniques,such as fuzzy logic, clustering, neural networks (NN), self-organizingmaps (SOM), and even simple threshold-base logic can be used, it is aninnovation of the present invention to utilize such techniques tocharacterize a driver's driving style. To illustrate how the stylecharacterization processor 52 works, an example of style classificationbased on fuzzy C-means (FCM) can be employed.

FIG. 9 is a flow chart diagram 160 showing such a fuzzy C-means processused by the style characterization processor 52. However, as will beappreciated by those skilled in the art, any of the before mentionedclassification techniques can be used for the style classification.Alternatively, the discriminants can be further separated into smallersets and classifiers can be designed for each set in order to reduce thedimension of the discriminant features handled by each classifier.

Data is collected at box 162, and the algorithm employed in the stylecharacterization processor 52 determines whether the variable data_readyis one at decision diamond 164, and if not, the process ends at block166. If data_ready is one at the decision diamond 164, the algorithmreads the recorded data from the data selection processor 48 at box 168and changes data_ready to zero at box 170. The algorithm then selectsdiscriminant features for the identified maneuver at box 172. Theprocess to select discriminate features can be broken down into threesteps, namely, deriving/generating original features from the collecteddata, extracting features from the original features, and selecting thefinal discriminate features from the extracted features. The algorithmthen selects the classifier for the particular maneuver and uses theselected classifier to classify the maneuver at box 174. The processorthen outputs the style (N) value, the time index N, the traffic indexTraffic_(index), the road condition index Road_(index) and the maneuveridentifier value M_(id) at box 176.

The traffic and road conditions can be incorporated in the stylecharacterization processor 52 using three different incorporationschemes. These schemes include a tightly-coupled incorporation thatincludes the traffic and road conditions as part of the features usedfor style classification, select/switch incorporation where multipleclassifiers come together with feature extraction/selection designed fordifferent traffic and road conditions and classifiers selected based onthe traffic and road conditions associated with the maneuver to beidentified, and decoupled-scaling incorporation where genericclassifiers are designed regardless of traffic and road conditions andthe classification results are adjusted by multiplying scaling factors.Tightly-coupled incorporation and selected/switch incorporation arecarried out in the style characterization processor 52 and thedecoupled-scaling incorporation can be included in either the stylecharacterization processor 52 or the decision fusion processor 56.

FIG. 10 is a block diagram of the style characterization processor 52,according to one embodiment of the present invention. The maneuveridentifier value M_(id) from the maneuver identification processor 46 isapplied to a switch 380 along with the recorded data from the dataselection processor 48, and the traffic condition index Traffic_(index)and the road condition index Road_(index) from the traffic/roadcondition recognition processor 50. The switch 380 identifies aparticular maneuver value M_(id), and applies the recorded data, thetraffic index Traffic_(index) and the road condition index Road_(index)to a style classification processor 382 for that particular maneuver.Each style classification processor 382 provides the classification forone particular maneuver. An output switch 384 selects the classificationfrom the processor 382 for the maneuvers being classified and providesthe style classification value to the style profile trip-logger 54 andthe decision fusion processor 56, as discussed above.

FIG. 11 is a block diagram of a style classification processor 390 thatemploys the tightly-coupled incorporation, and can be used for the styleclassification processors 382, according to an embodiment of the presentinvention. In this maneuver classifying scheme, the traffic indexTraffic_(index) and the road condition index Road_(index) are includedas part of the original feature vector. The processor 390 includes anoriginal feature processor 390 that receives the recorded data from thedata selection processor 48 and identifies the original features fromthe recorded data. The original features, the traffic indexTraffic_(index) and the road condition index Road_(index) are sent to afeature extraction processor 394 that extracts the features. When thefeatures are extracted for the particular maneuver, certain of thefeatures are selected by feature selection processor 396 and theselected features are classified by a classifier 398 to identify thestyle.

FIG. 12 is a block diagram of a style classification processor 400similar to the classification processor 390 which can be used as thestyle classification processors 382, where like elements are identifiedby the same reference numeral, according to another embodiment of thepresent invention. In this embodiment, the traffic index Traffic_(index)and the road condition index Road_(index) are applied directly to theclassifier 398 and not to the feature extraction processor 394. Thedifference between the classification processor 390 and theclassification processor 400 lies in whether the traffic indexTraffic_(index) and the road condition index Road_(index) are processedthrough feature extraction and selection. The design process of thefeature extraction/selection in the classifiers remains the sameregardless of whether the traffic index Traffic_(index) and the roadcondition index Road_(index) are included or not. However, the resultingclassifiers are different, and so is the feature extraction/selection ifthose indexes are added to the original feature vector.

FIG. 13 is a block diagram of a style classification processor 410 thatemploys the select/switch incorporation process, and can be used for thestyle classification processor 382, according to another embodiment ofthe present invention. In this embodiment, the classifier used forfeature extraction/selection is not only maneuver-type specific, butalso traffic/road condition specific. For example, the trafficconditions can be separated into two levels, light traffic and moderatetraffic, and the road conditions can be separated into good conditionand moderate condition. Accordingly, four categories are created for thetraffic and road conditions and a specific style classification isdesigned for each combination of the maneuver type and the fourtraffic-road condition categories. Once the maneuver has beenidentified, the style classification processor 410 selects theappropriate classification based on the traffic/road conditions. Theclassification includes the selection of the original features, featureextraction/selection and classifiers to classify the recorded maneuver.

In the style classification processor 410, the traffic indexTraffic_(index), the road condition index Road_(index) and the recordeddata from the data selection processor 48 for a particular maneuver aresent to an input switch 412. The recorded data is switched to aparticular channel 414 depending on the traffic and road indexcombination. Particularly, the combination of the traffic indexTraffic_(index) and the road condition index Road_(index) applied to theinput switch 14 will select one of four separate channels 414, includinga channel for light traffic and good road conditions, light traffic andmoderate road condition, moderate traffic and good road conditions, andmoderate traffic and moderate road conditions. For each traffic/roadindex combination, an original features processor 416 derives originalfeatures from the data associated with the maneuver, which is collectedby the data selection module 48, a feature extraction processor 418extracts the features from these original features, a feature selectionprocessor 420 further selects the features and a classifier 422classifies the driving style based on the selected features. An outputswitch 424 selects the style classification for the particularcombination of the traffic/road index.

In the select/switch incorporation scheme, the design of the stylecharacterization processor 52 is both maneuver-type specific andtraffic/road condition specific. Therefore, the maneuvers used for thedesign, which are collected from vehicle testing, are first groupedaccording to both the maneuver type and the traffic/road condition. Foreach group of maneuvers, i.e., maneuvers of the same type and with thesame traffic/road condition, the style classification, includingselection of original features, feature extraction/selection and theclassifiers, is designed. Since the style classification is designed forspecific traffic/road conditions, the traffic and road information is nolonger included in the features. Consequently, the design process wouldbe exactly the same as the generic design that does not taketraffic/road conditions into consideration. However, the resultingclassification will be different because the maneuvers are traffic/roadcondition specific. Moreover, the number of classifiers is four timesthat of the generic classifiers. As a result, the select/switchincorporation would require a larger memory to store the classifiers.

For the decoupled-scaling incorporation, the style classification designdoes not take traffic and road conditions into consideration. In otherwords, maneuvers of the same type are classified using the same originalfeatures, the same feature extraction/selection and the sameclassifiers. The original features do not include traffic/roadconditions. In other words, the style classification is generic totraffic/road conditions. The classification results are then adjustedusing scaling factors that are functions of the traffic/road conditions.For example, if the style classification of the Nth maneuver is style(N), where style (N) is a number representing a level of sporty driving,the adjusted style can be:

$\begin{matrix}{{{Style}_{adjust}(N)} = {{{style}(N)}{\kappa( {{{Traffic}_{index}(N)},{{Road}_{index}(N)}} )}}} & (11)\end{matrix}$Where κ (Traffic_(index), Road_(index)) is the scaling factor related totraffic/road conditions.

Alternatively, the affects of the traffic and road conditions may bedecoupled, for example by:

$\begin{matrix}{{{Style}_{adjust}(N)} = {{{Style}(N)}{\alpha( {{Traffic}_{index}(N)} )}{\beta( {{Road}_{index}(N)} )}}} & (13)\end{matrix}$

The adjusted style is:

$\begin{matrix}{{\kappa( {{Traffic}_{index},{Road}_{index}} )} = {{\alpha( {Traffic}_{index} )}{\beta( {Road}_{index} )}}} & (12)\end{matrix}$

The scaling factors are designed so that the sportiness level isincreased for maneuvers under a heavier traffic and/or worse roadcondition. For example, if the sportiness is divided into five levelswith 1 representing a conservative driving style and 5 representing avery sporty driving style, than Style(N) ε {0, 1, 2, 3, 4, 5} with 0representing hard-to-decide patterns. Therefore, one possible choice forthe scaling factors can be:

$\begin{matrix}{{\alpha( {Traffic}_{index} )} = \{ \begin{matrix}{1,} & {{{for}\mspace{14mu}{Traffic}_{index}} \leq {Traffic}_{light}} \\{{1.5 \times \frac{{Traffic}_{index} - {Traffic}_{light}}{{Traffic}_{heavy} - {Traffic}_{light}}},} & \begin{matrix}{{{for}\mspace{14mu}{Traffic}_{light}} <} \\{{Traffic}_{index} < {Traffic}_{heavy}}\end{matrix}\end{matrix} } & (14) \\{{\beta( {Road}_{index} )} = \{ \begin{matrix}{1,} & {{{for}\mspace{14mu}{Road}_{index}} \geq {Road}_{good}} \\{{1.5 \times \frac{{Road}_{good} - {Road}_{index}}{{Road}_{good} - {Road}_{bad}}},} & \begin{matrix}{{{for}\mspace{14mu}{Road}_{bad}} <} \\{{Road}_{index} < {Road}_{good}}\end{matrix}\end{matrix} } & (15)\end{matrix}$Note that if style (N)=0, style_(adjust)(N) remains zero.

Equation (14) or (15) will also work if the style characterization ofthe Nth maneuver outputs a confidence vector instead of a scalarstyle(N)=[conf(0) conf(1) . . . conf(k)]^(T), where conf(i) is theconfidence the classifier has in that input pattern belongs to the classc_(i). In this case, the scaling factors in equations (14) and (15) areno longer scalars, but matrixes.

The style characterization processor 52 can also use headway controlbehaviors to utilize the data corresponding to three of the fivemaneuvers, particularly, vehicle following, another vehicle cutting in,and preceding vehicle changing lanes. The other two maneuvers, nopreceding vehicle and the subject vehicle changing lanes, are either oflittle concern or involve more complicated analysis.

The vehicle following maneuver can be broken down into three types ofevents based on the range rate, i.e., the rate change of the followingdistance, which can be directly measured by a forward-looking radar orprocessed from visual images from a forward-looking camera. Three typesof events are a steady-state vehicle following where the range rate issmall, closing in, where the range rate is negative and relativelylarge, and falling behind, where the range rate is positive andrelatively large. Thus, the data for vehicle following can be portionedaccordingly based on the range rate.

During steady-state vehicle following, the driver's main purpose inheadway control is to maintain his or her headway distance of headwaytime, i.e., the time to travel the headway distance. Therefore, theacceleration and deceleration of the subject vehicle mainly depends onthe acceleration and deceleration of the preceding vehicle, while theheadway distance/time is a better reflection of the driver's drivingstyle. Hence, the average headway distance, or headway time, the averagevelocity of the vehicle, the traffic index Traffic_(index) and the roadcondition index Road_(index), including the road type index and ambientcondition index, are used as the original features in theclassification. With these original features, various feature extractionand feature selection techniques can be applied so that the resultingfeatures can best separate patterns of different classes. Varioustechniques can be used for feature extraction/selection and are wellknow to those skilled in the art. Since the original features, and thusthe extracted features, consist of only five features, all features canbe selected in the feature selection process. A neural network can bedesigned for the classification where the network has an input layerwith five input neurons corresponding to the five discriminants, ahidden layer and an output layer with 1 neuron. The output of the netranges from 1-5, with 1 indicating a rather conservative driver, 3 atypical driver and 5 a rather sporty driver. The design and training ofthe neural network is based on vehicle test data with a number ofdrivers driving under various traffic and road conditions.

During the closing-in period, the signals used for classification arethe range rate, the time to close the following distance, i.e., therange divided by the range rate, vehicle acceleration/deceleration andvehicle speed. The decrease of the following distance may be due to thedeceleration of the preceding vehicle or the acceleration of the subjectvehicle. Therefore, the style index should be larger if it is due to theacceleration of the subject vehicle. Because all of these signals aretime-domain series, data reduction is necessary in order to reduce thecomplexity of the classifier. One selection of original featuresincludes the minimum value of the headway distance, the minimum value ofthe range rate because the range rate is now negative, the minimum valueof the time to close the gap, i.e., the minimum headway distance/rangerate, the average speed, the average longitudinal acceleration, and thetraffic and road indexes. Similarly, a neural network can be designedwith six neurons in the input layer and one in the output layer. Again,the design and training of the neural network is based on vehicle testdata with drivers driving under various traffic and road conditions.

The falling-behind event usually occurs when the subject vehicle has notresponded to the acceleration of the preceding vehicle or the subjectvehicle simply chooses to decelerate to have a larger followingdistance. The former case may not reflect the drivers style while thesecond case may not add much value since the larger following distancewill be used in vehicle following. Hence, no further processing isnecessary for this event.

Another vehicle cutting in and preceding vehicle changing lanes are twomaneuvers that induce a sudden change in the headway distance/time wherethe driver accelerates or decelerates so that the headway distance/timereturns to his or her desired value. The acceleration and decelerationduring such events can reflect driving style.

When another vehicle cuts in, the subject vehicle usually deceleratesuntil the headway distance/time reaches the steady-state headwaydistance/time referred by the driver. A more conservative driver usuallydecelerates faster to get back to his/her comfort level quicker, while asportier driver has a higher tolerance of the shorter distance anddecelerates relatively slowly. Factors that contribute to the driver'sdecision of how fast/slow to decelerate include the difference between anew headway distance/time and his/her preferred headway distance/time,as well as vehicle speed and road conditions. An exemplary selection oforiginal features consists of the difference between the new headwaytime, which is the headway time at the instant the cut-in occurs, andthe driver preferred headway time, i.e., an average value from thevehicle-following maneuver, the time to reach the preferred headwaytime, which can be determined by the settling of the headway time andrange rate, the maximum range rate, the maximum braking force, themaximum variation in speed ((average speed-minimum speed)/averagespeed), average speed and the road condition index. Similarly, neuralnetworks can be used for the classification.

When the preceding vehicle changes lanes, the following distancesuddenly becomes larger. A sportier driver may accelerate quickly andclose the gap faster, while a more conservative driver acceleratesslowly and gradually closes the gap. Similar to the case above, theoriginal features include the difference between the new headway time,which is the headway time at the instance the preceding vehicle changesout of the lane, and the driver's preferred headway time, the time toreach the preferred headway time, the maximum range rate, the maximumthrottle, the maximum variation and speed ((maximum speed-averagespeed)/average speed), average speed, and the road condition indexRoad_(index). Again, neural networks can be designed for thisclassification.

It is noted that although neural networks can be used as theclassification technique, the style characterization processor 52 caneasily employ other techniques, such as fuzzy logic, clustering, simplethreshold-base logic, etc.

The maneuvers related to driver's headway control behavior show that thecharacteristic maneuvers can be properly identified given variousin-vehicle measurements, including speed, yaw rate, lateralacceleration, steering profile and vehicle track using GPS sensors. Oncea characteristic maneuver is identified, key parameters can beestablished to describe such a maneuver and the intended path can bereconstructed. With this information available, the intended path can beprovided to a process maneuver model where human commands of a typicaldriver can be generated. The maneuver model can be constructed based ona dynamic model of a moderate driver. One example of a construction anduse of such a dynamic model is disclosed U.S. patent application Ser.No. 11/398,952, titled Vehicle Stability Enhancement Control Adaptationto Driving Skill, filed Apr. 6, 2006, assigned to the assignee of thisapplication and herein incorporated by a reference.

FIG. 14 is a system 330 showing an example of such a process maneuvermodel. Vehicle data from a vehicle 332 is collected to be qualified andidentified by a maneuver qualification and identification processor 334.Once the data is qualified and the maneuver is identified, a maneuverindex and parameter processor 336 creates an index and furtheridentifies relevant parameters for the purpose of reconstruction of theintended path. These parameters can include the range of yaw rate,lateral acceleration the vehicle experienced through the maneuver,vehicle speed, steering excursion and the traffic condition indexTraffic_(index). The maneuver index processor 336 selects theappropriate maneuver algorithm 338 in a path reconstruction processor340 to reproduce the intended path of the maneuver without consideringthe specificities of driver character reflected by the unusual steeringagility or excessive oversteer or understeer incompatible with theintended path. The one or more maneuvers are summed by a summer 342 andsent to a maneuver model processor 344. Driver control command inputsincluding steering, braking and throttle controls are processed by adriver input data processor 346 to be synchronized with the output ofthe maneuver model processor 344, which generates the correspondingcontrol commands of steering, braking and throttle controls of anaverage driver. The control signal from the maneuver model processor 344and the driver input data processor 346 are then processed by a driverstyle diagnosis processor 348 to detect the driving style at box 350.

FIG. 15 is a block diagram of a system 360 showing one embodiment as tohow the driving style diagnosis processor 348 identifies the differencesbetween the driver's behavior and an average driver. The maneuver modelcommand inputs at box 362 for the maneuver model processor 344 are sentto a frequency spectrum analysis processor 364, and the driver commandinputs at box 366 from the driver input data processor 346 are sent to afrequency spectrum analysis processor 368. The inputs are converted tothe frequency domain by the frequency spectrum analysis processors 364and 368, which are then sent to a frequency content discrepancy analysisprocessor 370 to determine the difference therebetween. However, it isnoted that other methodologists can be applied to identify thedifference between the model and the commands besides frequency domainanalysis.

FIG. 16 is a graph with frequency on the horizontal axis and magnitudeon the vertical axis illustrating a situation where behavioraldifferences are identified through the variation of the frequencyspectrum. Given a headway control maneuver, the driver may apply thebrake in different ways according to a specific driving style. While anaverage driver results in the spectrum in one distribution, anotherdriver, such as driver-A, shows a higher magnitude in the low-frequencyarea and lower magnitude in the high-frequency area. Driver-B shows theopposite trend. The differences in these signal distributions can beused to determine the driving style of the specific driver.

The difference in the frequency spectrum distribution can be used asinputs to a neural network where properly trained persons can identifythe proper style of the driver. The art of using neural networks toidentify the driving style given the differences of the frequencyspectrum distribution is well-known to those skilled in the art, andneed not be discussed in further detail here. In this illustration, aproperly trained neural network classifier can successfully characterizedriver-A as conservative and driver-B as aggressive if the difference ison the spectrum distribution is determined to have completed apredetermined threshold.

The style characterization processor 52 classifies driving style basedon every single characteristic maneuver and the classification resultsare stored in a data array in the style profile trip-logger 54. Inaddition, the data array also contains information such as the timeindex of the maneuver M_(seq), the type of maneuver identified by theidentifier value M_(id), the traffic condition index Traffic_(index) andthe road condition index Road_(index). The results stored in thetrip-logger 54 can be used to enhance the accuracy and the robustness ofthe characterization. To fulfill this task, the decision fusionprocessor 56 is provided. Whenever a new classification result isavailable, the decision fusion processor 56 integrates the new resultwith previous results in the trip-logger 54. Various decision fusiontechniques, such as a Bayesian fusion and Dempster-Shafer fusion, can beused and applied in the decision fusion processor 56. To demonstrate howthis works, a simple example of weighted-average based decision is givenbelow.

The decision fusion based on a simple weighted average can be given as:

$\begin{matrix}{{{Style}_{fused}(N)} = {\sum\limits_{t = {N - k}}^{N}{{\alpha( {{Traffic}_{index}(i)} )}{\beta( {{Road}_{index}(i)} )}{\gamma( {{M\_ ID}(i)} )}\lambda^{N - i}{{style}(i)}}}} & (16)\end{matrix}$Or equivalently:

$\begin{matrix}{{{Style}_{fused}(N)} = {{{\alpha( {{Traffic}_{index}(N)} )}{\beta( {{Road}_{index}(N)} )}{\gamma( {{M\_ ID}(N)} )}{{style}(N)}} + {\lambda\;{{Style}_{fused}( {N - 1} )}}}} & (17)\end{matrix}$Where N is the time index of the most recent maneuver, style(i) is thestyle classification result based on the ith maneuver, i.e., M_seq=i,∝(Traffic_(index)(i)) is a traffic-related weighting, β(Road_(index)(i))is a road condition related weighting, γ(M_ID(i)) is a maneuver-typerelated weighting, λ is a forgetting factor (0<λ≦1) and k is the lengthof the time index window for the decision fusion.

In one embodiment, traffic and road conditions have already beenconsidered in the style classification process, the decision fusion maynot need to incorporate their effect explicitly. Therefore,∝(Traffic_(index)(i)) and β(Road_(index)(i)) can be chosen as 1.Moreover, if the classification results from different maneuvers arecompatible with one another, γ(M_ID(i)) can also be chosen as 1. Thedecision fusion can then be simplified as:Style_(fused)(N)=style(N)+λStyle_(fused)(N−1)  (18)Recommended values for the forgetting factors λ are between 0.9 and 1,depending on how much previous results are valued. Of course, thedecision fusion can also take into consideration traffic, road andmaneuver types and use the form of equation (16).

As discussed above, the maneuver identification processor 46 recognizescertain maneuvers carried out by the vehicle driver. In one embodiment,the style classification performed in the style characterizationprocessor 52 is based on a vehicle lane-change maneuver identified bythe processor 46. Lane-change maneuvers can be directly detected oridentified if a vehicles in-lane position is available. The in-laneposition can be derived by processing information from theforward-looking camera 20, or a DGPS with sub-meter level accuracytogether with the EDMAP 28 that has lane information. Detection of lanechanges based on vehicle in-lane position is well-known to those skilledin the art, and therefore need not be discussed in significant detailherein. Because forward-looking cameras are usually available in luxuryvehicles and mid-range to high-range DGPS are currently rare inproduction vehicles, the present invention includes a technique todetect lane change based on common in-vehicle sensors and GPS. Thoughthe error in a GPS position measurement is relatively large, such as 5-8meters, its heading angle measurement is much more accurate, and can beused for the detection of lane changes.

In a typical lane-change maneuver, a driver turns the steering wheel toone direction, then turns towards the other direction, and then turnsback to neutral as he/she completes the lane change. Since the vehicleyaw rate has an approximately linear relationship with the steeringangle in the linear region, it exhibits a similar pattern during a lanechange. Mathematically, the vehicle heading direction is the integrationof vehicle yaw rate. Therefore, its pattern is a little different.During the first half of the lane change when the steering wheel isturning to one direction, the heading angle increases in the samedirection. During the second half of the lane-change maneuver, thesteering wheel is turned to the other direction and the heading angledecreases back to approximately its initial position.

Theoretically, lane-change maneuvers can be detected based on vehicleyaw rate or steering angle because the heading angle can be computedfrom vehicle yaw rate or steering angle. However, the common in-vehiclesteering angle sensors or yaw rate sensors usually have a sensor biasand noise that limit the accuracy of the lane-change detection.Therefore, vehicle heading angle is desired to be used together with thesteering angle or yaw rate. It can be recognized that a lane change is aspecial type of a steering-engaged maneuver. To keep the integrity ofthe data associated with an identified maneuver, the system keepsrecording and refreshing a certain period of data, such as T=2 s.

FIG. 17 is a flow chart diagram 90 showing an operation of the maneuveridentification processor 46 for detecting lane-change maneuvers,according to an embodiment of the present invention. At a start block92, the maneuver identifying algorithm begins by reading the filteredvehicle speed signal v, the filtered vehicle yaw rate signal ω and thefiltered vehicle heading angle Φ from the signal processor 44. Thealgorithm then proceeds according to its operation states denoted by twoBoolean variables Start_flag and End_flag, where Start_flag isinitialized to zero and End_flag is initialized to one. The algorithmthen determines whether Start_flag is zero at block 94, and if so, thevehicle 10 is not in a steering-engaged maneuver. The algorithm thendetermines if any steering activities have been initiated based oncertain conditions at block 96, particularly:max|ω(t−T:t)|≧ω_(small)|Φ(t−T)|≧Φ_(small)  (19)

If the conditions of the block 96 are met, the algorithm sets Start_flagto one and End_flag to zero at box 98. The algorithm then sets astarting time t_(start) of the maneuver, and defines the initial headingangle Φ_(ini) and an initial lateral position y at box 100 as:Φ_(ini)=Φ(t−T)  (20)y=∫ _(t−T) ^(t) v _(x)(τ)*Sin(Φ(τ))dτ  (21)

If the conditions of the block 96 are not met, then the vehicle 10 isnot involved in a steering-engaged maneuver and Start_flag remains zero,where the process ends at block 102.

The algorithm then returns to the start block 92. If Start_flag is oneat the block 94, as set at the block 98, the vehicle 10 is now in asteering-engaged maneuver. If the vehicle 10 is in a steering-engagedmaneuver, i.e., Start_Flag=1, the algorithm then determines whether themaneuver has been determined to be a curve-handling maneuver. To dothis, the algorithm determines whether the maneuver identifier valueM_(id) is one at block 104. If the value M_(id) is not one at the block104, then the maneuver has not been determined to a curve-handlingmaneuver yet. The algorithm then determines if the maneuver is acurve-handling maneuver at block 106 by examining whether:|ω(t)≧ω_(med) |y|≧y _(large)|Φ(t)−Φ_(ini)|≧Φ_(large)  (22)In one non-limiting embodiment, ω_(med) is 15°, Φ_(large) is 45° andy_(large) is 10 m.

If all of the conditions at block 106 are met, then the maneuver is acurve-handling maneuver and not a lane-changing maneuver. The algorithmthen will set the maneuver identifier value M_(id) equal to one at block108 to indicate a curve-handling maneuver.

If all of the conditions are not met at the block 106, then thealgorithm updates the vehicle lateral position y at block 110 as:y=y+v _(x)(t)*sin(Φ(t))*Δt  (23)Where Δt is the sampling time.

The algorithm then determines whether the maneuver is complete at block112 by:|Φ(t−t ₂ :T)−Φ_(ini)|>Φ_(small)  (24)Where if T₂≦T the maneuver is regarded as being complete.

If the condition of block 112 is satisfied, then the algorithmdetermines whether the following condition is met at block 114:∥y|−4|<y_(small)  (25)Where y_(small) is 4 m in one non-limiting embodiment to allow anestimation error and t−t_(start)>t_(th). If the condition of the block114 is met, the maneuver is identified as a lane-change maneuver, wherethe value M_(id) is set to two and the time is set to t_(end) at box116. Otherwise, the maneuver is discarded as a non-characteristicmaneuver, and the value M_(id) is set to zero at box 118. Start_flag isthen set to zero and End_flag is set to one at box 120.

If the maneuver identifier value M_(id) is one at the block 104, themaneuver has been identified as a curve-handling maneuver and not alane-change maneuver. The algorithm then determines at box 122 whether:max|ω(t−T:t)|≦ω_(small)  (26)If this condition has been met, then the curve-handling maneuver hasbeen completed, and the time is set to t_(end) at box 124, Start_flag isset to zero and End_flag is set to one at the box 120. The process thenreturns to the start box 92.

It is noted that the maneuver identifier processor 46 may not detectsome lane changes if the magnitude of the corresponding steeringangle/yaw rate or heading angle is small, such as for some lane changeson highways. The missed detection of these types of lane changes willnot degrade the lane-change based style characterization since theyresemble straight-line driving.

As discussed herein, the present invention provides a techniqueutilizing sensor measurements to characterize a driver's driving style.Lane-change maneuvers involve both vehicle lateral motion andlongitudinal motion. From the lateral motion point of view, the steeringangle, yaw rate, lateral acceleration and lateral jerk can all reflect adrivers driving style. The values of those signals are likely to belarger for a sporty driver than those for a conservative driver.Similarly, from the perspective of longitudinal motion, the distance ittakes to complete a lane change, the speed variation, the decelerationand acceleration, the distance the vehicle is to its preceding vehicle,and the distance the vehicle is to its following vehicle after a lanechange also reflects the driver's driving style. These distances arelikely to be smaller for a sporty driver than those for a conservativedriver. Consequently, these sensor measurements can be used to classifydriving style. However, those signals are not suitable to be useddirectly for classification for the following reasons. First, a typicallane change usually lasts more than five seconds. Therefore, thecollected data samples usually amount to a considerable size. Datareduction is necessary in order to keep the classification efficient andeconomic. Second, the complete time trace of the signals is usually noteffective for the classification because it usually degrades theclassification performance because a large part of it does not representthe patterns and is simply noise. In fact, a critical design issue inclassification problems is to derive/extract/select discriminantfeatures, referred to as discriminants which best represent individualclasses. As a result, the style characterization processor 52 includestwo major parts, namely a feature processor and a style classifier, asdiscussed above.

The feature processor derives original features based on the collecteddata, extracts features from the original features, and then selects thefinal features from the extracted features. The main objective ofderiving original features is to reduce the dimension of data input tothe classifier and to derive a concise representation of the pattern forclassification. With these original features, various feature extractionand feature selection techniques can be used so that the resultingfeatures can best separate patterns of different classes. Varioustechniques can be used for feature extraction/selection and are wellknow to those skilled in the art. However, the derivation of originalfeatures typically relies on domain knowledge. The present inventionderives the original features based on engineering insights. However,the discussion below of deriving the original features, or originaldiscriminates, should not limit the invention as described herein.

The following original features/discriminants for classifying alane-change maneuver are chosen based on engineering insights and canbe, for example:

-   -   1. The maximum value of the yaw rate        max(|ω(t_(start):t_(end))|);    -   2. The maximum value of the lateral acceleration        max(|a_(y)(t_(start):t_(end))|);    -   3. The maximum value of the lateral jerk max(|{dot over        (a)}_(y)(t_(start):t_(end))|);    -   4. The distance for the lane change to be completed ∫_(t)        _(start) ^(t) ^(end) v_(x)(t)dt;    -   5. The average speed mean(v_(x)(t_(start):t_(end)));    -   6. The maximum speed variation        max(v_(x)(t_(start):t_(end)))−min(v_(x)(t_(start):t_(end)));    -   7. The maximum braking pedal force/position (or the maximum        deceleration);    -   8. The maximum throttle percentage (or the maximum        acceleration);    -   9. The minimum distance (or headway time) to its preceding        vehicle (e.g., from a forward-looking radar/lidar or camera, or        from GPS with V2V communications);    -   10. The maximum range rate to its preceding vehicle if available        (e.g., from a forward-looking radar/lidar or camera, or from GPS        together with V2V communications); and    -   11. The minimum distance (or distance over speed) to the        following vehicle at the lane the vehicle changes to, if it is        available e.g., from a forward-looking radar/lidar or camera, or        from GPS with V2V communications).

Variations of the discriminant features listed above may be known tothose skilled in the art. Because the system 40 only has access toinformation related to the discriminants 1-10 identified above, thecorresponding classifier uses only discriminants 1-10. Otherembodiments, such as the systems 60 and 80, can use all of thediscriminants.

Feature extraction and feature selection techniques can then be appliedto the original features/discriminants to derive the finalfeatures/discriminates, which will be discussed in further detail below.One vector X_(i)[x_(i1) x_(i2) . . . x_(iN)] for the final discriminantscan be formed corresponding to each lane-change maneuver where irepresents the ith lane-change maneuver and N is the dimension of thefinal discriminants. This discriminate vector will be the input to theclassifier. As mentioned before, various techniques can be used todesign the classifier, for example, fuzzy C-means (FCM) clustering. InFMC-based classification, each class consists of a cluster. The basicidea of the FCM-based classification is to determine the class of apattern, which is represented by a discriminant vector, based on itsdistance to each pre-determined cluster center. Therefore, theclassifier first calculates the distances:D _(ik) =∥X _(i) −V _(k)∥² _(A)=(X _(i) −V _(k))A(x _(i) −V _(k))^(T),1≦k≦C  (27)Where Vk is the center vector of cluster k, A is an N×N matrix thataccounts for the shape of the pre-determined clusters, C is the totalnumber of pre-determined clusters, such as C=3˜5 representing thedifferent levels of sporty driving. The cluster centers Vk and thematrix A are determined during the design phase.

Based on the distances, the algorithm further determines the membershipdegree of the curved discriminant vector as:

$\begin{matrix}{{\mu_{ik} = \frac{1}{\sum\limits_{j - 1}^{c}( {D_{ik}/D_{ij}} )^{2/{({m - 1})}}}},{1 \leq k \leq C}} & (28)\end{matrix}$Where m is a weighting index that is two in one non-limiting embodiment.

The corresponding lane-change maneuvers are classified as class j if:μ_(ij)=max(μ_(ik))(1≦k≦C)  (29)

Alternatively, the classifier can simply use a hard partition andclassify the corresponding lane-change maneuver as the class that yieldsthe smallest distance, such as:

$\begin{matrix}\{ \begin{matrix}{{\mu_{ij} = 1},} & {{{if}\mspace{14mu} D_{ij}} = {\min( {D_{ik},{1 \leq k \leq C}} )}} \\{{\mu_{ij} = 0},} & {{{if}\mspace{14mu} D_{ij}} > {\min( {D_{ik},{1 \leq k \leq C}} )}}\end{matrix}  & (30)\end{matrix}$

For the style characterization processor 52 to operate properly, thecluster center Vx and the matrix A need to be predetermined. This can beachieved during the design phase based on vehicle test data with anumber of drivers driving under various traffic and road conditions Thelane changes of each participating driver can be recognized as describedin the maneuver identifier processor 46 and the corresponding data canbe recorded by the data selection processor 48. For each lane change,the discriminant vector X_(i)=[x_(i1) x_(i2) . . . x_(iN)] can bederived.

Combining all of the discriminant vectors into a discriminant matrix Xgives:

$\begin{matrix}{X = \begin{bmatrix}x_{11} & x_{12} & \cdots & x_{1N} \\x_{21} & x_{22} & \cdots & x_{21} \\\vdots & \vdots & \ddots & \vdots \\x_{M\; 1} & x_{M\; 2} & \cdots & x_{MN}\end{bmatrix}} & (31)\end{matrix}$

The matrix A can be an N×N matrix that accounts for difference variancesin the direction of the coordinate axes of X as:

$\begin{matrix}{A = \begin{bmatrix}( {1/\sigma_{1}} )^{2} & 0 & \cdots & 0 \\0 & ( {1/\sigma_{2}} )^{2} & \cdots & 0 \\\vdots & \vdots & \ddots & \vdots \\0 & 0 & \cdots & ( {1/\sigma_{N}} )^{2}\end{bmatrix}} & (32)\end{matrix}$

The cluster center can be determined by minimizing an objective functionreferred to as C—means functional as:

$\begin{matrix}{{J( {{X;U},V} )} = {\sum\limits_{k = 1}^{c}{\sum\limits_{i = 1}^{M}{( \mu_{ik} )^{m}{{X_{i} - V_{k}}}_{A}^{2}}}}} & (33)\end{matrix}$The minimization of such a function is well known, and need not bedescribed in further detail herein. It is noted that although fuzzyclustering is used as the classification technique in this embodimentfor classifying the lane-change maneuver, the present invention caneasily employ other techniques, such as fuzzy logic, neural networks,SOM, or threshold-based logic.

The maneuver identification processor 46 can identify other types ofcharacteristic maneuvers. According to another embodiment of the presentinvention, the maneuver identification processor 46 identifiesleft/right-turn maneuvers, which refer to maneuvers where a vehicleturns from one road to another that is approximately perpendicular.Left/right-turns usually occur at intersections and a vehicle may or maynot be fully stopped depending on the intersection traffic.Left/right-turn maneuvers can be identified based on the driverssteering activity and the corresponding change in vehicle headingdirection.

FIG. 18 is a flow chart diagram 180 showing a process performed by themaneuver identification processor algorithm to identify aleft/right-turn maneuver. In this non-limiting example, left/right-turnsare regarded as a special type of steering-engaged maneuvers whereleft/right-turns are accompanied with a relatively large maximum yawrate or steering angle and an approximately 90° change in vehicleheading direction. To keep the integrity of the data associated with themaneuver, the system keeps recording and refreshing at a certain period,for example, T=2 s, of data.

In FIG. 18, the maneuver identifier algorithm begins with reading thefiltered vehicle speed signal v and the filtered yaw rate signal ω fromthe signal processor 44 at block 182. The algorithm then proceedsaccording to its operation states denoted by the two Boolean variablesStart_flag and End_flag, where Start_flag is initialized to zero andEnd-flag is initialized to one. If Start_flag is zero, then the vehicle10 is not performing a steering-engaged maneuver. The algorithmdetermines whether Start_flag is zero at block 84 and, if so, determineswhether ω(t)≧ω_(med) at decision diamond 186, where ω_(med) is 2° persecond in one non-limiting embodiment. If this condition is met, thenthe vehicle 10 is likely entering a curve or starting a turn, soStart_flag is set to one and End_flag is set to zero at box 188. Thealgorithm then sets timer t_(start)=t−T, and computes the heading angleΦ=ω((t)×Δt) at box 190, where Δt is the sampling time.

If Start_flag is not zero at the block 184 meaning that the vehicle 10is in a steering-engaged maneuver, the algorithm then determines whetherthe maneuver has been completed. Upon completion of the steering-engagedmaneuver, the algorithm determines whether the steering-engaged maneuverwas a left/right-turn or a curve-handling maneuver at block 192 bydetermining whether max(ω(t−T:t))≦ω_(small), where ω_(small) is 1° inone non-limiting embodiment. If this condition has been met, thesteering-engaged maneuver has been completed, so the algorithm setsStart_flag to zero, End_flag to one and time t_(end)=t-T at box 194.

The algorithm then determines whethermax(|ω(t_(start):t_(end))|)≧ω_(large) at block 196 and, if not, sets theidentifier value M_(id) to zero at box 198 because the yaw rate is toosmall indicating either the curve is too mild or the vehicle 10 isturning very slowly. Thus, the corresponding data may not reveal much ofa driving style, so the data is discarded. In one non-limitingembodiment, ω_(large) is 7° per second. If the condition of the block196 is met, meaning that the curve is significant enough, the algorithmdetermines whether 75°≦|Φ|≦105° and determines whether timet_(end)-t_(start)<t_(th) at the decision diamond 200. In onenon-limiting embodiment, time threshold t_(th) is 15 seconds. If both ofthese conditions are met, then the algorithm determines that aleft/right-turn has been made and sets the maneuver value M_(id) to 2 atbox 202.

If either of these conditions has not been met at the decision diamond200, then the algorithm determines that the maneuver is a curve-handlingmaneuver and not a left/right-turn maneuver, and thus sets the maneuvervalue M_(id) to 1 at box 204 indicating the curve-handling maneuver.

If the condition of block 192 has not been met, the vehicle 10 is stillin the middle of a relatively large yaw motion or turn, and thus, thealgorithm updates the heading angle at box 206 as Φ=Φ+ω(t)×Δt. As themaneuver identification processor 46 determines the beginning and end ofthe maneuver, the data selection processor 48 stores the correspondingdata segment based on the variables Start_flag, End_flag, t_(start) andt_(end).

The style classification consists of two processing steps, namelyfeature processing that derives discriminant features based on thecollected data and classification that determines the driving stylebased on the discriminants. The first step, feature processing, reducesthe dimension of the data so as to keep the classifier efficient and thecomputation economic. Feature processing is also critical because theeffectiveness of the classification depends heavily on the selection ofthe right discriminants. These discriminants are then used as the inputto the classifier. Various classification techniques, such as fuzzylogic, neural networks, self-organizing maps, and simple threshold-basedlogic can be used for the style classification. The discriminants arechosen based on engineering insights and decision tree based classifiersare designed for the classification.

In this embodiment for classifying a left/right-turn maneuver, the stylecharacterization processor 52 receives the maneuver value M_(id) as twofrom the maneuver identification processor 46 and the styleclassification processor 52 selects the corresponding processclassification to process this information. As above, the stylecharacterization processor 52 includes two processing steps. Theleft/right-turn maneuver involves both lateral motion and longitudinalmotion. The lateral motion is generally represented by the steeringangle, the yaw rate and the lateral acceleration. Typically, thesportier a driver is, the larger these three signals are. Thelongitudinal motion is usually associated with the throttle and brakinginputs and the longitudinal acceleration. Similarly, the sportier thedriver is, the larger these three signals can be. Therefore, all sixsignals can be used for style classification. Accordingly, the followingoriginal features/discriminants can be chosen for classifying aleft/right-turn maneuver:

-   -   1. The maximum lateral acceleration a_(y max)=max        (a_(y)(t_(start):t_(end)));    -   2. The maximum yaw rate ω_(max)=max(ω(t_(start):t_(end)));    -   3. The maximum longitudinal acceleration        a_(x max)=max(a_(x)(t_(start):t_(end)));    -   4. The maximum throttle opening        Throttle_(max)=max(Throttle(t_(start):t_(end))); and    -   5. The speed at the end of the turn v_(x)(t_(end)).

If the vehicle 10 starts turning without stopping fully(min(v_(x)(t_(start):t_(end))))<2 m/s, the maximum brakingforce/position Braking_(max)=max(Braking(t_(start):t_(end))) and theminimum speed min(v_(x)(t_(start):t_(end))) during the turn are includedas the original features/discriminants.

For simplicity, the feature extraction and feature selection processescan be removed and the original features can be used directly as thefinal features/discriminates. These discriminants can be input to adecision tree for style classification by the processor 52. Decisiontrees are classifiers that partition the feature data on one feature ata time. A decision tree comprises many nodes connected by branches wherenodes that are at the end of branches are called leaf nodes. Each nodewith branches contains a partition rule based on one discriminant andeach leaf represents the sub-region corresponding to one class. Thefeature data representing the left/right turns used for classificationis labeled according to the leaves it reaches through the decision tree.Therefore, decision tress can be seen as a hierarchical way to partitionthe feature data.

FIG. 19 shows a classification decision tree 210 including nodes 212. Aroot node 214 of the tree has two branches, one for turns from a stopand the other for turns without a stop. For turns from a stop, thesubsequent nodes employ the following partition rulesa_(ymax)<a_(ysmall1), a_(ymax)≧a_(ylarge1),Throttle_(max)≧Throttle_(large1) and a_(ymax)≧a_(ylarge2), and for turnswithout a full stop, the partition rules are a_(ymax)<a_(ysmall2),a_(ymax)≧a_(ylarge2), Throttle_(max)>Throttle_(large2) andBraking_(max)≧Braking_(large). The leaf nodes 216 at the end of thebranches 218 represent five driving classes labeled from 1 to 5 in theorder of increasing driving aggressiveness. Note that all of thediscriminants mentioned in the feature extraction are used in theexemplary decision tree 210. Further, the decision tree can be expandedto include more discriminants.

The thresholds in the partition rules are predetermined based on vehicletest data with a number of drivers driving under various traffic androad conditions. The design and tuning of decision-tree basedclassifiers are well-known to those skilled in the art and furtherdetails need not be provided for a proper understanding. It is notedthat although the decision tree is used as the classification techniquefor classifying a left/right-turn maneuver, the present invention caneasily employ other techniques, such as fuzzy logic, clustering andthreshold-based logic to provide the classification.

According to another embodiment of the present invention, the maneuveridentification processor 46 identifies a U-turn maneuver. A U-turnmaneuver refers to performing a 180° rotation in order to reversedirection of traffic. According to the traffic or geometric design,U-turn maneuvers can be roughly divided into three types, namely, aU-turn from a near-zero speed, continuous U-turns at the end ofstraight-line driving and interrupted U-turns at the end ofstraight-line driving. The first type usually happens at intersectionswhere U-turns are allowed. The vehicle first stops at the intersectionand then conducts a continuous U-turn to reverse direction. Because thevehicle starts from a near-zero speed and the U-turn is a rather tightmaneuver, such a U-turn may not be affective in providing a driver'sdriving style.

The second type usually occurs when there is no traffic sign and theopposite lane is available. This type of U-turn can reveal a driversdriving style through the drivers braking control and the vehicledeceleration right before the U-turn and the vehicle yaw and lateralacceleration during the U-turn. To perform a U-turn of the third type,the vehicle would turn about 90° and then wait until the opposite lanesbecome available to continue the U-turn.

The third type of U-turn may or may not be useful in reviewing thedrivers driving style depending on the associated traffic scenarios. Forexample, if the opposite traffic is busy, the vehicle may need to waitin line and move slowly during the large portion of the U-turn. In suchsituations, even a sporty driver will be constrained to driveconservatively.

The present invention focuses mainly on the second type of U-turn, i.e.,a continuous U-turn at the end of straight-line driving. However,similar methodologies can be easily applied to the other types ofU-turns for the style characterization. A U-turn maneuver can beidentified based on the drivers steering activity in the correspondingchange in the vehicle heading direction.

An example of the recognition of a vehicle U-turn maneuvers, togetherwith recognition of curve-handling maneuvers can also be provided by theflow chart diagram 180. In this example, the U-turn maneuver is regardedas a special type of left/right-turn maneuver where the U-turn isaccompanied with a relatively large maximum yaw rate or steering angleand an approximately 180° change in the vehicle heading direction. Tokeep the integrity of the data associated with an identified maneuver,the system keeps recording and refreshing a certain period, for example,T=2 s, of data.

As with the left/right-turn maneuver discussed above, the maneuver valueM_(id)=0 represents a non-characteristic maneuver that will not be usedfor style characterization, M_(id)=1 is for a curve-handling maneuverand M_(id)=2 is for a U-turn maneuver. Instead of the range of 75°-105°for the heading angle Φ for the left/right-turn maneuver at decisiondiamond 200, it is determined whether the heading angle Φ is between165° and 195° for the U-turn maneuver.

As discussed above, the style characterization processor 52 receives themaneuver identifier value M_(id) from the processor 46. A U-turnmaneuver involves both lateral motion and the longitudinal motion. Thelateral motion is generally represented by the steering angle, the yawrate and the lateral acceleration. Typically, the sportier the driveris, the larger these three signals can be. The longitudinal motion isusually associated with throttle and braking inputs and the longitudinalacceleration. Similarly, the sportier the driver, the larger thesesignals typically are. Therefore, all six signals can be used for stylecharacterization in the processor 52.

The collected data is typically not suitable to be used directly forstyle characterization because the collected data consist of the timetrace of those signals, which usually results in a fair amount of data.For example, a typical U-turn maneuver lasts more than five seconds.Therefore, with a 10 Hz sampling rate, more than 50 samples of eachsignal would be recorded. Therefore, data reduction is necessary inorder to keep the classification efficient. Also, the complete timetrace of those signals is usually not effective for thecharacterization. In fact, a critical design issue in classificationproblems is to derive/extract/select discriminative features that bestrepresent individual classes.

Thus, the style characterization processor 52 includes a featureprocessor and a style classifier. As mention above, the featureprocessor derives original features based on the collected data,extracts features from the original features and then selects the finalfeatures from the extracted features. Feature extraction tries to createnew features based on transformations or combinations of the originalfeatures and the feature selection selects the best subset of the newfeatures derived through feature extraction. The original features areusually derived using various techniques, such as time-series analysisand frequency-domain analysis These techniques are well-known to thoseskilled in the art. The present invention describes a straight forwardway to derive the original discriminant features based on engineeringinsights.

For the six signals referred to above, the original discriminants forclassifying a U-turn maneuver can be chosen as:

-   -   1. The maximum lateral acceleration a_(y max)=max        (a_(y)(t_(start):t_(end)));    -   2. The maximum yaw rate ω_(max)=max(ω(t_(start):t_(end)));    -   3. The speed at the beginning of the U-turn v_(x)(t_(start));    -   4. The minimum speed during the U-turn        v_(x min)=min(v_(x)(t_(start):t_(end)));    -   5. The speed at the end of the U-turn v_(x)(t_(end));    -   6. The maximum braking force/position        Braking_(max)=max(Braking(t_(start):t_(end)));    -   7. An array of braking index BI_(braking)=[BI₁ . . . BI_(i) . .        . BI_(N)] based on the distribution of the brake pedal        position/force;    -   8. The maximum longitudinal acceleration        a_(x max)=max(a_(x)(t_(start):t_(end)));    -   9. The maximum throttle opening        Throttle_(max)=max(Throttle(t_(start):t_(end))); and    -   10. An array of throttle index TI_(throttle)=[TI₁ . . . TI_(i) .        . . TI_(N)], based on the distribution of the throttle opening.

Each braking index BI_(i) is defined as the percentage of the time whenthe braking pedal position/force is greater than a threshold B_(thi).That is, if the U-turn maneuver takes time T_(total) seconds and duringthat period of time the braking pedal position/force is greater thanB_(thi) for T_(i) seconds, then the braking indexBI_(i)=T_(i)/T_(total). Alternatively, the time T_(total) can be definedas a time when the braking is greater than the braking threshold(Braking>B_(th)), where the threshold B_(th) is smaller than thethreshold B_(thi). Similarly, each throttle index TI_(i) is defined asthe percentage of the time when the throttle opening a is greater than athreshold a_(thi). Suitable examples of the threshold a_(thi) can be20%, 30%, 40%, 50% and 60% or from 10% to 90% with a 10% intervalin-between. In summary, the total number of discriminants for a U-turnmaneuver can be n=8+2N or more if additional discriminants, such astraffic and road indexes, are included.

For each recognized vehicle U-turn maneuver, one set of the originalfeatures is derived. This set of original features can be represented asan original feature vector x, an n-dimension vector with each dimensionrepresenting one specific feature. This original feature vector servesas the input for further feature extraction and feature selectionprocessing. Feature extraction tries to create new features based ontransformations or combination of the original features (discriminants),while feature selection selects the best subset of the new featuresderived through feature extraction.

Various feature extraction methods can be used for classifying a U-turnmaneuver, such as Principle Component Analysis (PCA), LinearDiscriminant Analysis (LDA), Kernel PCA, Generalized DiscriminantAnalysis (GDA), etc. In one non-limiting embodiment, LDA is used, whichis a linear transformation where y=U^(T)x, and where U is an n-by-nmatrix and y is an n-by-1 vector with each row representing the value ofthe new feature. The matrix U is determined off-line during the designphase. Note that the LDA transformation does not reduce the dimension ofthe features.

To further reduce the feature dimension for improved classificationefficiency and effectiveness, various feature selection techniques, suchas Exhaustive Search, Branch-and-Bound Search, SequentialForward/Backward Selection and Sequential Forward/Backward FloatingSearch, can be used. The subset that yields the best performance ischosen as the final features to be used for classification. For example,the resulting subset may consist of m features corresponding to the {i₁i₂ . . . i_(m)}(1≦i₁≦i₂≦ . . . ≦i_(m)≦n) row of the feature vector y. Bywriting the matrix U as u=[u₁ u₂ . . . u_(n)] with each vector being ann-by-1 vector, and then selecting only the vectors corresponding to thebest subset, yields W=[u_(i1) u_(i2) . . . u_(im)], an M-by-N matrix.Combining the feature extraction and feature selection, the finalfeatures corresponding to the original feature vector x can be derivedas z=W^(T)x.

The style characterization processor 52 then classifies the driversdriving style for the U-turn maneuver based on the discriminant featurevector z. Classification techniques, such as fuzzy logic, clustering,neural networks (NN), support vector machines (SVM), and simplethreshold-based logic can be used for style classification. In oneembodiment, an SVM-based classifier is used. The standard SVM is atwo-class classifier, which tries to find an optimal hyperplane, i.e.,the so-called decision function, that correctly classifies trainingpatterns as much as possible and maximizes the width of the marginbetween the classes. Because the style classification involves more thantwo classes, a multi-class SVM can be employed to design the classifier.A K-class SVM consists of K hyper-planes: f_(k)(z)=W_(k)z+b_(k), k=1, 2,. . . , k where w_(k) and b_(k) are determined during the design phasebased on the test data. The class label c for any testing data is theclass whose decision function yields the largest output as:

$\begin{matrix}{{c = {{\text{arg}{\max\limits_{k}{{fx}(z)}}} = {\text{arg}{\max\limits_{k}( {{w_{k}z} + b_{k}} )}}}},{k = 1},2,\ldots\;,K} & (34)\end{matrix}$

The feature extraction, feature selection and the K-class SVM aredesigned off-line based on vehicle test data. A number of drivers wereasked to drive several instrumented vehicles under various trafficconditions and the sensor measurements were collected for theclassification design. For every vehicle U-turn maneuver, an originalvector x can be constructed. All of the feature vectors corresponding tovehicle U-turn maneuvers are put together to form a training matrixX=[y₁ y₂ . . . y_(L)], where L is the total number of vehicle U-turnmaneuvers. Each row of the matrix X represents the values of one featurevariable while each column represents the feature vector of a trainingpattern. The training matrix X is then used for the design of the styleclassification based on vehicle U-turn maneuvers.

The feature extraction is based on LDA, a supervised feature extractiontechnique. Its goal is to train the linear data projection Y=U^(T)X suchthat the ratio of the between-class variance to the within-classvariance is maximized, where X is an n-by-L matrix and U is an n-by-nmatrix. Accordingly, Y=[y₁ y₂ . . . y_(L)] is an n-by-L matrix, wherethe new feature vector y_(i) still consists of n features. Commercial oropen-source algorithms that compute the matrix U are available andwell-known to those skilled in the art. The inputs to those algorithmsinclude the training matrix X and the corresponding class labels. In oneembodiment, the class labels can be 1-5 with 1 indicating a conservativedriver, 3 indicating a typical driver and 5 being a sporty driver. Inaddition, a class label 0 can be added to represent those hard-to-decidepatterns. The class labels are determined based on expert opinions byobserving the test data. The outputs of the LDA algorithms include thematrix U and the new feature matrix Y.

The feature selection is conducted on the feature matrix Y. In thisparticular application, because the dimension of the extracted featuresis relatively small, an Exhaustive Search can be used to evaluate theclassification performance of each possibly combination of the extractedfeatures. The new features still consist of n features, and there areΣ_(i−1) ^(n)C^(i) _(n) possible combinations of the n features. TheExhaust Search evaluates the classification performance of each possiblecombination by designing an SVM based on the combination and derivingthe corresponding classification error. The combination that yields thesmallest classification error is regarded as the best combination wherethe corresponding features (i₁ i₂ . . . i_(m)) determine the matrix[u_(i1) u_(i2) . . . u_(im)]. Conveniently, the SVM corresponding to thebest feature combination is the SVM classifier. Since commercial oropen-source algorithms for SVM designs are well-known to those skilledin the art, a detailed discussion is not necessary herein.

It is noted that although SVM is used as the classification technique inthis embodiment, the present invention can easily employ othertechniques, such as fuzzy logic, clustering or simple threshold-basedlogics for classifying U-turn maneuvers. Similarly, other featureextraction and feature selection techniques can be easily employedinstead of the LDA and Exhaustive Search.

According to another embodiment of the present invention, the maneuveridentification processor 46 identifies a vehicle passing maneuver. Atthe beginning of a vehicle passing maneuver, the subject vehicle (SV),or passing vehicle, approaches and follows a slower preceding objectvehicle (OV), which later becomes the vehicle being passed. If thedriver of the SV decides to pass the slower OV and an adjacent lane isavailable for passing, the driver initiates the first lane change to theadjacent lane and then passes the OV in the adjacent lane. If there isenough clearance between the SV and the OV, the driver of the SV mayinitiate a second lane change back to the original lane. Because thestyle characterization based on vehicle headway control behavior alreadyIncludes the vehicle approaching maneuver, the vehicle approachingbefore the first lane change is not included as part of the passingmaneuver. As a result, the passing maneuver starts with the first lanechange and ends with the completion of the second lane change.Accordingly, a passing maneuver can be divided into three phases,namely, phase one consists of the first lane change to an adjacent lane,phase two is passing in the adjacent lane and phase three is the secondlane change back to the original lane. In some cases, the second phasemay be too short to be regarded as an independent phase, and in othercases, the second phase may last so long that it may be more appropriateto regard the passing maneuver as two independent lane changes. Thisembodiment focuses on those passing maneuvers where a second phase isnot too long, such as less than T_(th) seconds.

The detection of a passing maneuver then starts with the detection of afirst lane change. The lane changes can be detected using vehiclesteering angle or yaw rate together with vehicle heading angle from GPSas described above for the embodiment identifying lane-change maneuvers.Alternatively, a lane change can be detected based on image processingfrom a forward-looking camera, well-known to those skilled in the art.

The end of the first lane change is the start of the second phase, i.e.,passing in the adjacent lane. The second phase ends when a second lanechange is detected. If the SV changes back to its original lane within acertain time period, such as T_(th) seconds, the complete maneuverincluding all three of the phases is regarded as a vehicle passingmaneuver. If the SV changes to a lane other than its original lane, thecomplete maneuver may be divided and marked as individual lane-changemaneuvers for the first and third phases. If a certain time passes andthe SV does not initiate a second lane change, the maneuver is regardedas uncompleted, however, the first phase may still be used as anindividual lane-change maneuver.

Based on the discussion above, FIG. 20 is a flow chart diagram 220showing a process for identifying a vehicle passing maneuver, accordingto an embodiment of the present invention. To keep the integrity of thedata associated with an identified maneuver, the system keeps recordingand refreshing at a certain period, such as T=2 s, of data.

The maneuver identifying algorithm begins with reading the filteredvehicle speed signal v and the filtered vehicle yaw rate signal ω fromthe signal processor 44 at box 222. The maneuver identifying algorithmthen proceeds using the Boolean variables Start_flag and End_flag, whereStart_flag is initialized to zero and End_flag is initialized to one.The algorithm then determines whether Start_flag is zero at block 224 todetermine whether the vehicle 10 is in a passing maneuver. If Start_flagis zero at the block 224, then the algorithm determines whether a lanechange has started at decision diamond 226 to determine whether thepassing maneuver has started, and if not, returns at box 228 forcollecting data. If the algorithm determines that a lane change hasstarted at the decision diamond 226, which may be the first lane changein a passing maneuver, the algorithm sets Start_flag to one, End_flag tozero, the phase to one and timer T_(start)=t at box 470.

If Start_flag is not zero at the block 224 meaning that the maneuver hasbegun, then the algorithm determines whether the maneuver is in thefirst phase at decision diamond 472. If the maneuver is in the firstpassing phase at the decision diamond 472, then the algorithm determineswhether a lane change has been aborted at block 474. If the lane changehas not been aborted at the block 474, the algorithm determines whetherthe lane change has been completed at block 476, and if not returns tothe block 228 for collecting data. If the lane change has been completedat the block 476, the algorithm sets the phase to two, the timet_(1end)=t and the time t_(2start)=t+Δt at box 478. If the lane changehas been aborted at the block 474, meaning that the passing maneuver hasbeen aborted, then the algorithm sets the maneuver identifier valueM_(id) to zero at box 480, and sets Start_flag to zero, End_flag to oneand the phase to zero at box 482.

If the passing maneuver is not in the first phase at the decisiondiamond 472, then the algorithm determines whether the passing maneuveris in the second phase at decision diamond 484. If the passing maneuveris not in the second phase at the decision diamond 484, the passingmaneuver is already in its third phase, i.e., the lane change back tothe original lane. Therefore, the algorithm determines whether this lanechange has been aborted at the decision diamond 486, and if so, sets themaneuver identifier value Mid to zero at the box 480, and Start_flag tozero, End_flag to one and phase to zero at the box 482.

If the lane change back has not been aborted at the decision diamond486, the algorithm determines whether the lane change has been completedat decision diamond 488, and if not, returns to box 228 for collectingdata. If the lane change has been completed at the decision diamond 488,the algorithm sets the maneuver identifier value M_(id) to one, timet_(3end)=t, time t_(start)=t_(start) and time t_(end)=t_(3end) at box490, and sets Start_flag to zero, End_flag to one and the phase to zeroat the box 482.

If the passing maneuver is in the second phase at the decision diamond44, the algorithm determines whether there has been a lane change backto the original lane at decision diamond 492, and if so, sets thepassing maneuver phase to three, time t_(2en)=t and time t_(3start)=t+Δtat box 494. If a lane change back has not started at the decisiondiamond 492, then the algorithm determines whether the condition timet-t_(2start)>T_(th) has been met at decision diamond 496, and if not,returns to the box 228. If the condition of the decision diamond 492 hasbeen met, then too much time has passed for a passing maneuver, and thealgorithm sets the maneuver identifier value M_(id) to zero at box 498,and sets Start_flag to zero, End_flag to one and the phase to zero atthe box 482.

As the maneuver identifier value M_(id) determines the beginning and theend of a maneuver, the data selector 48 stores that data correspondingto the maneuver based on the variables Start_flag, End_flag, M_(id),t_(start) and t_(end). When the maneuver identifier value M_(id) is setfor a vehicle passing maneuver, the data collected is sent to the stylecharacterization processor 52, and the driver's driving style for thatmaneuver is classified. The first and third phases of a vehicle passingmaneuver are lane changes. During a lane change, the sportier driver ismore likely to exhibit larger values in vehicle steering angle, yawrate, lateral acceleration and lateral jerk. Similarly, from theperspective of a longitudinal motion, a sportier driver usuallycompletes a lane change in a shorter distance and exhibits a largerspeed variation and deceleration/acceleration, a shorter distance to itspreceding vehicle before the lane change, and a shorter distance to thefollowing vehicle after the lane change. The second phase of a vehiclepassing maneuver, passing in the adjacent lane, involves mostlylongitudinal control. A driver's driving style can be revealed by howfast he/she accelerates, the distance the vehicle traveled during thesecond phase or the time duration, and the speed difference between thesubject vehicle and the object vehicle.

Accordingly, a number of discriminants for classifying a passingmaneuver can be selected based on this information. For the first phase,i.e., the first lane change, the original discriminant features can bedefined as:

-   -   1. The maximum value of the yaw rate:        max(|w(t_(1start):t_(1end))|);    -   2. The maximum value of lateral acceleration        max(|a_(y)(t_(1start):t_(1end))|);    -   3. The maximum value of lateral jerk max(|{dot over        (a)}_(y)(t_(1start):t_(1end))|);    -   4. The distance for the lane change to be completed ∫_(t)        _(1start) ^(t) ^(1end) v_(x)(t)dt;    -   5. The average speed mean(|v_(x)(t_(1start):t_(1end))|);    -   6. The maximum speed variation        max(|v_(x)(t_(1start):t_(1end))|)−min(|v_(x)(t_(1start):t_(1end))|);    -   7. The maximum braking pedal force/position (or the maximum        deceleration);    -   8. The maximum throttle percentage (or the maximum        acceleration);    -   9. The minimum distance (or headway time) to its preceding        vehicle, i.e., from a forward-looking radar/lidar or camera, or        from GPS together with V2V communications;    -   10. The maximum range rate to its preceding vehicle if        available, i.e., from a forward-looking radar/lidar or camera,        or from GPS together with V2V communications; and    -   11. The minimum distance (or distance over speed) to the        following vehicle at the lane the vehicle changes to, if it is        available, i.e., from side radar/camera, or GPS with V2V        communications.

For the second phase, the original discriminant features can be:

-   -   1. The maximum throttle percentage        max(|throttle(t_(2start):t_(2end))|) (or longitudinal        acceleration max(|a_(x)(t_(2start):t_(2end))|);    -   2. The average throttle percentage;    -   3. The distance traveled ∫_(t) _(2start) ^(t) ^(2end)        v_(x)(t)dt; and    -   4. The maximum speed variation        max(|v_(x)(t_(2start):t_(2end))|)−min        (|v_(x)(t_(2start):t_(2end))|).

For the third phase, i.e., the second lane change, the original featuresare similar to those for the first phase with t_(1start) and t_(1end)replaced with t_(3start) and t_(3end). In addition, the total distancethe subject vehicle traveled during a passing maneuver can also be addedas a discriminant. In summary, the total number of discriminants for onepassing maneuver can be n=10+4+10+1=25 or n=11+4+11+1=27 if the distanceto the following vehicle is available.

For each recognized vehicle passing maneuver, one set of the originalfeatures is derived. This set of original features can be represented asan original feature vector x, an n-dimension vector with each dimensionrepresenting one specific feature. This original feature vector servesas the input for further feature extraction and feature selectionprocessing.

As mentioned above, various feature extraction methods can be used forclassifying a passing maneuver, such as Principle Component Analysis(PCA), Linear Discriminant Analysis (LDA), Kernel PCA, GeneralizedDiscriminant Analysis (GDA), etc. In one non-limiting embodiment, LDA isused, which is a linear transformation where y=U^(T)x, and where U is ann-by-n matrix and y is an n-by-1 vector with each row representing thevalue of the new feature. The matrix U is determined off-line during thedesign phase.

To further reduce the feature dimension for improved classificationefficiency and effectiveness, feature selection techniques are appliedto find the subset that yields the best performance is chosen as thefinal features to be used for classification. For example, the resultingsubset may consist of m features corresponding to the {i₁ i₂ . . .i_(m)}(1≦i₁≦i₂≦ . . . ≦i_(m)≦n) row of the feature vector y. By writingthe matrix U as u=[u₁ u₂ . . . u_(n)] with each vector being an n-by-1vector, and then selecting only the vectors corresponding to the bestsubset, yields W=[u_(i1) u_(i2) . . . u_(im)], an m-by-n matrix.Combining the feature extraction and feature selection, the finalfeatures corresponding to the original feature vector x can be derivedas z=W^(T)x.

The style characterization processor 52 then classifies the driver'sdriving style based on the discriminant feature vector z. Classificationtechniques, such as fuzzy logic, clustering, neural networks (NN),support vector machines (SVM), and simple threshold-based logic can beused for style classification. In one embodiment, an SVM-basedclassifier is used. Because the style classification involves more thantwo classes, a multi-class SVM can be employed to design the classifier.A K-class SVM consists of K hyper-planes: f_(k)(z)=w_(k)z+b_(k), k=1, 2,. . . , k where w_(k) and b_(k) are determined during the design phasebased on the test data. The class label c for any testing data is theclass whose decision function yields the largest output as:

$\begin{matrix}{{c = {{\text{arg}{\max\limits_{k}{{fx}(z)}}} = {\text{arg}\;{\max\limits_{k}( {{w_{k}z} + b_{k}} )}}}},{k = 1},2,\ldots\;,K} & (35)\end{matrix}$

The feature extraction, feature selection and the K-class SVM aredesigned off-line based on vehicle test data. A number of drivers wereasked to drive several instrumented vehicles under various trafficconditions and the sensor measurements were collected for theclassification design. For every vehicle passing maneuver, an originalfeature vector x can be constructed. All of the feature vectorscorresponding to vehicle passing maneuvers are put together to form atraining matrix X=[x₁ x₂ . . . x_(L)], where L is the total number ofvehicle passing maneuvers. Each row of the matrix X represents thevalues of one feature variable while each column represents the featurevector of a training pattern. The training matrix X is then used for thedesign of the style classification based on vehicle passing maneuvers.

The feature extraction is based on LDA, a supervised feature extractiontechnique. Its goal is to train the linear data projection Y=U^(T)X suchthat the ratio of the between-class variance to the within-classvariance is maximized, where X is an N-by-L matrix and U is an N-by-Nmatrix. Accordingly, Y=[y₁ y₂ y_(L)] is an N-by-L matrix, where the newfeature vector y_(i) still consists of n features. Commercial oropen-source algorithms that compute the matrix U are available andwell-known to those skilled in the art. The inputs to those algorithmsinclude the training matrix X and the corresponding class labels. In oneembodiment, the class labels can be 1-5 with 1 indicating a conservativedriver, 3 indicating a typical driver and 5 being a sporty driver. Inaddition, a class label 0 can be added to represent those hard-to-decidepatterns. The class labels are determined based on expert opinions byobserving the test data. The outputs of the LDA algorithms include thematrix U and the new feature matrix Y.

The feature selection is conducted on the feature matrix Y. In thisparticular application, because the dimension of the extracted featuresis relatively small, an Exhaustive Search can be used to evaluate theclassification performance of each possibly combination of the extractedfeatures. The new features still consist of n features, and there areΣ_(t−1) ^(n) C^(i) _(n) possible combinations of the n features. TheExhaust Search evaluates the classification performance of each possiblecombination by designing an SVM based on the combination and derivingthe corresponding classification error. The combination that yields thesmallest classification error is regarded as the best combination wherethe corresponding features {i₁ i₂ . . . i_(m)} determine the matrix[u_(i1) u_(i2), . . . u_(im)]. Conveniently, the SVM corresponding tothe best feature combination is the SVM classifier. Since commercial oropen-source algorithms for SVM designs are well-known to those skilledin the art, a detailed discussion is not necessary herein.

It is noted that although SVM is used as the classification technique inthis embodiment for classifying passing maneuvers, the present inventioncan easily employ other techniques, such as fuzzy logic, clustering orsimple threshold-based logic. Similarly, other feature extraction andfeature selection techniques can be easily employed instead of the LDAand Exhaustive Search.

According to another embodiment of the present invention, the maneuveridentification processor 46 also identifies characteristic maneuvers ofvehicles at highway on/off ramps. Typical highway on-ramps start with ashort straight entry, continue to a relatively tight curve, and then endwith a lane merging. Typical highway off-ramps start with a lane splitas the entry portion, continue to a relatively tight curve, and then ashort straight road portion and end at a traffic light or a stop sign.Although highway on/off ramps without a curve portion do exist, mostmaneuvers at highway on/off ramps involve both curve-handling and arelatively long period of acceleration or deceleration. Consequently,maneuvers at highway on/off ramps can be identified based on steeringactivities, or vehicle yaw motion, and the corresponding change in thevehicle speed.

An example of a process for identifying highway on/off-ramp maneuvers isshown by flow chart diagram 230 in FIGS. 21A and 21B, according to anembodiment of the present invention. In this example, the entry portionof the on/off ramp is ignored. That is, on/off ramp maneuvers start withcurve handling and vehicle yaw motion, or other steering activities, todetermine the start of the maneuver. The on-ramps are determined basedon the speed variation after the curve portion and the off-ramps aredetermined based on the speed variation during and after the curveportion. To keep the integrity of the data associated with an identifiedmaneuver, the process keeps recording and refreshing at certain periods,such as T=2 s, of data. Alternately, if the vehicle is equipped with aforward-looking camera or a DGPS with an enhanced digital map, theinformation can be incorporated or used independently to determine whenthe vehicle is at a highway on/off ramp. Usage of that information forthe determination of highway on/off ramps is straight forward andwell-known to those skilled in the art.

Returning to FIGS. 21A and 21B, the maneuver identifier processor 46begins by reading the filtered vehicle speed signal v and the filteredvehicle yaw rate signal c from the signal processor 44 at box 232. Themaneuver identifier algorithm then proceeds using the Boolean variablesStart_flag, End_flag and End_curve_flag, where Start_flag is initializedto zero, End_flag is initialized to one and End_curve_flag isinitialized to one. The algorithm determines whether Start_flag is zeroat decision diamond 234 to determine whether the vehicle 10 is in ahighway on/off ramp maneuver. If Start_flag is zero at the decisiondiamond 234, then the algorithm determines whether the conditionω(t)≧ω_(med) has been met at decision diamond 236, where ω_(med) can be2° per second in one non-limiting embodiment to determine whether thevehicle 10 is likely entering the curve or starting to turn. If thecondition of the decision diamond 236 is not met, then the algorithmreturns at block 238 to collecting the data. If the condition of thedecision diamond 236 is met, meaning that the vehicle is entering acurve or starting a turn, the algorithm sets Start_flag to one, End_flagto zero, End_curve_flag to zero, timer t_(start)=t−T, and the maneuveridentifier value M_(id) to zero at block 240. The algorithm then returnsat the block 238 to collecting data.

If Start_flag is not zero at the decision diamond 234, meaning that thevehicle 10 is in a potential highway on/off ramp maneuver, then thealgorithm determines whether End_curve_fag is zero at decision diamond242. If End_curve_flag is zero at the decision diamond 242, meaning thatthe vehicle 10 is in the curve portion of the potential on/off rampmaneuver, the algorithm then determines whether the curve portionmaneuver has been completed. Particularly, the algorithm determineswhether the condition max(ω(t−T:t))≦ω_(small) has been met at decisiondiamond 244, and if so, meaning that the curve portion maneuver has beencompleted, sets End_curve_flag to one and time t_(end) _(—) _(curve)=t−Tat block 246. In one non-limiting embodiment, ω_(small) is 1° persecond.

The algorithm also determines vehicle speed information, particularly,whether the condition v_(x)(t)−v_(x)(t_(start))≦−v_(max) is met atdecision diamond 248, and if so, meaning that the curve portion ispossibly part of an off-ramp maneuver, sets the maneuver identifiervalue M_(id) to 2 at box 250. If the conditions of the decision diamonds244 and 248 are not met, then the algorithm returns to collecting dataat block 238 where the vehicle 10 is still in the middle of a relativelylarge yaw motion and thus, the processor 46 waits for the next datareading. If the condition of the decision diamond 248 is not met, thecurve-handling maneuver might be part of an on-ramp maneuver, where themaneuver identifier value M_(id) stays at zero. In one non-limitingexample, the speed v_(max) can be 25 mph.

If End_curve_flag is one at the decision diamond 242, meaning that thecurve portion has been completed, the algorithm determines whether timet−t_(end) _(—) _(curve)>T_(large) at block 252, for example,T_(large)=30 s. If this condition is met, the potential on/off rampmaneuver has not ended after a relatively long time, so the maneuver isdiscarded by setting the maneuver identifier value M_(id) to zero at box254 and setting Start_flag to zero and End_flag to one at box 256.

If the condition of the block 252 is not met, the algorithm determineswhether the maneuver has been identified as an off-ramp maneuver bydetermining whether the maneuver identifier value M_(id) is two atdecision diamond 258. If the maneuver identifier value M_(id) is one orzero, the on-ramp maneuver ends when the increase in the vehicle speedbecomes smaller. Therefore, if the maneuver identifier value M_(id) isnot two at the decision diamond 258, the algorithm determines whetherthe speed condition v_(x)(t)−v_(x)(t−aT)≦v_(med) is met at decisiondiamond 260, where aT is 10 s and v^(med) is 5 mph in one non-limitingexample. If this condition is not met, meaning the on-ramp maneuver hasnot ended, then the algorithm returns to the block 238.

If the condition of the decision diamond 260 has been met, the algorithmdetermines whether the speed conditions v_(x)(t−T)≧V_(large) andv_(x)(t−T)−v_(x)(t_(start))≦v_(th) have been met at decision diamond262. In one non-limiting embodiment, V_(large) is 55 mph and v_(th) is20 mph. If both of the conditions of the decision diamond 262 have beenmet, then the maneuver is truly an on-ramp maneuver. The algorithm setsthe maneuver identifier value M_(id) to one identifying an on-rampmaneuver and sets time t_(end)=t−T at box 264, and Start_flag to zeroand End_flag to one at the box 256 and returns at the block 238. If thecondition of the decision diamond 262 has not been met, the maneuver isnot an on-ramp maneuver, so the maneuver is discarded by setting themaneuver identifier value Mid to zero at the box 254, and Start_flag tozero and End_flag to one at the box 256, and returning at the block 238.

If the maneuver identifier value M_(id) is two at the decision diamond258, the off-ramp maneuver ends if the vehicle speed v is very small.Therefore, the algorithm determines whether the speed conditionv_(x)(t−T:t)≦v_(small) is met at decision diamond 266, where v_(small)is 3 mph in one non-limiting example. If this condition of the decisiondiamond 266 has been met, meaning that the off-ramp maneuver has ended,then the algorithm sets time t_(end)=t−T at box 268, Start_flag to zeroand End_flag to one at box 256, and returns at the block 238.

If the condition of the decision diamond 266 has not been met, thealgorithm determines whether the speed has not gone down enough toindicate that the maneuver is not an off-ramp maneuver by determiningwhether the speed condition v_(x)(t)>v_(x)(t_(end) _(—) _(curve))+10 mphhas been met at decision diamond 270. If this condition is met, meaningthat the speed is too high for the maneuver to be an off-ramp maneuver,the maneuver identifier value M_(id) is set to zero at box 272, andStart_flag is set to zero and End_flag is set to one at the box 256, andthe algorithm returns at the block 238. If the condition of the decisiondiamond 270 has not been met, meaning that the potential off-rampmaneuver has not been completed, then the algorithm returns at the block238.

As the maneuver identifier processor 46 determines the beginning and theend of a maneuver, the data selection processor 48 stores thecorresponding data segment based on the variables Start_flag, End_flag,t_(start) and t_(end).

Highway on/off-ramp maneuvers involve both curve-handling and arelatively large speed increase/decrease. In general, the sportier adriver is, the larger the lateral acceleration and the yaw rate are onthe curves. Similarly, the sportier a driver is, the faster the speedincreases at an on-ramp. However, at an off-ramp, a conservative drivermay decelerate fast at the beginning to have a lower speed while asportier driver may postpone the deceleration to enjoy a higher speed atthe off-ramp and then decelerate fast at the end of the off-ramp. Inaddition, a sportier driver may even engage throttle at an off-ramp tomaintain the desired vehicle speed. Thus, the steering angle, yaw rateand the lateral acceleration can be used to assess sportiness of thecurve-handling behavior at an on/off-ramp, and vehicle speed,longitudinal acceleration, throttle opening and brake pedalforce/position can be used to assess the drivers longitudinal control.

However, the data collected consists of the time trace of the signals,which usually results in a fair amount of data. For example, a typicalon/off-ramp maneuver lasts more than 20 seconds. Therefore, with a 10 Hzsampling rate, more than 200 samples of each signal would be recorded.Thus, data reduction is necessary in order to keep the classificationefficient. Further, the complete time trace of the signals is usuallynot affective for the classification. In fact, a critical design issuein classification problems is to extract discriminate features, whichbest represent individual classes. As a result, the stylecharacterization processor 52 may include a feature processor and astyle classifier, as discussed above.

As discussed above, the feature processor involves three processingsteps, namely, original feature derivation, feature extraction andfeature selection. The original features are usually derived usingvarious techniques, such as time-series analysis and frequency-domainanalysis, which are well understood to those skilled in the art. Thepresent invention proposes a non-limiting technique to derive theoriginal features based on engineering insights.

For on-ramp maneuvers, the original features include the maximum lateralacceleration, the maximum yaw rate, the average acceleration, themaximum throttle opening and an array of throttleindexesTI_(throttle)=[TI₁ . . . TI_(i) . . . TI_(N)] based on thedistribution of the throttle opening. Each throttle index TI_(i) isdefined as the percentage at the time when the throttle opening a isgreater than a threshold a_(thi). That is, if the on-ramp maneuver takesT_(total) seconds and during that time period the throttle opening isgreater than a_(thi) (0<a_(thi)<100%) for T_(i) seconds, then thethrottle index TI_(i)=T_(i)/T_(total). Examples of the thresholds[a_(th1) . . . a_(thi) . . . a_(thN)] can include [20% 30% 40% 50% 60%]or from 10% to 90% with a 10% interval in between. Alternatively,T_(total) can be defined as the time when a>a_(th), where a_(th) shouldbe smaller than a_(thi) or i=1, 2, . . . , N.

For off-ramp maneuvers, the original features include the maximumlateral acceleration, the maximum yaw rate, the average deceleration,the maximum braking pedal position/force and an array of braking indexesBI_(braking)=[BI₁ . . . BI_(i) . . . BI_(N)] based on the distributionof the brake pedal position/force. Similar to the throttle index TI_(i),the braking index BI_(i) is defined as the percentage of the time whenthe braking pedal position/force b is greater than a threshold b_(thi).

For each recognized on/off-ramp maneuver, one set of the originalfeatures is derived. This set of original features can be represented asan original feature vector x, an n-dimension vector with each dimensionrepresenting one specific feature. This original feature vector servesas the input for further feature extraction and feature selectionprocessing. Feature extraction tries to create new features based ontransformations or combination of the original features (discriminants),while feature selection selects the best subset of the new featuresderived through feature extraction.

Various feature extraction methods can be used, such as PrincipleComponent Analysis (PCA), Linear Discriminant Analysis (LDA), KernelPCA, Generalized Discriminant Analysis (GDA), etc. In one non-limitingembodiment, LDA is used, which is a linear transformation wherey=U^(T)x, and where U is an n-by-n matrix and y is an n-by-1 vector witheach row representing the value of the new feature. The matrix U isdetermined off-line during the design phase. Because the originalfeatures for highway on-ramp and off-ramp maneuvers are different, thefeature extraction would also be different. That is, the matrix U foron-ramp maneuvers would be different from the matrix U for off-rampmaneuvers.

To further reduce the feature dimension for improved classificationefficiency and effectiveness, feature selection techniques, such asExhaustive Search, can be used. The subset that yields the bestperformance is chosen as the final features to be used forclassification. For example, the resulting subset may consist of mfeatures corresponding to the {i₁ i₂ . . . i_(m)}(1≦i₁≦i₂≦ . . .≦i_(m)≦n) row of the feature vector y. By writing the matrix U as u=[u₁u₂ . . . u_(m)] with each vector being an n-by-1 vector, and thenselecting only the vectors corresponding to the best subset, yieldsW=[u_(i1) u_(i2) . . . u_(im)], an M-by-N matrix. Combining the featureextraction and feature selection, the final features corresponding tothe original feature vector x can be derived as z=W^(T)x. Once again,the matrix W for on-ramp maneuvers would be different from that foroff-ramp maneuvers.

The style characterization processor 52 then classifies the driversdriving style based on the discriminant feature vector z. Classificationtechniques, such as fuzzy logic, clustering, neural networks (NN),support vector machines (SVM), and simple threshold-based logic can beused for style classification. In one embodiment, an SVM-basedclassifier is used. A K-class SVM consists of K hyper-planes:f_(k)(z)=w_(k)z+b_(k), k=1, 2, . . . , k where w_(k) and b_(k) aredetermined during the design phase based on the test data. The classlabel c for any testing data is the class whose decision function yieldsthe largest output as:

$\begin{matrix}{{c = {{\text{arg}{\max\limits_{k}{{fx}(z)}}} = {\text{arg}{\max\limits_{k}( {{w_{k}z} + b_{k}} )}}}},{k = 1},2,\ldots\;,K} & (36)\end{matrix}$The SVM parameters for on-ramp maneuvers are different from those foroff-ramp maneuvers.

The feature extraction, feature selection and the K-class SVM aredesigned off-line based on vehicle test data. A number of drivers wereasked to drive several instrumented vehicles under various trafficconditions and the sensor measurements were collected for theclassification design. Highway on/off-ramp maneuvers are recognizedusing the maneuver identification algorithm discussed above. For everyon/off-ramp maneuver, an original feature vector x can be constructed.The feature vector corresponding to all the on-ramp maneuvers are puttogether to form a training matrix X_(on)=[x_(1on) x_(2on) . . .x_(Lon)], where L_(on) is the total number of on-ramp maneuvers. Eachrow of the matrix X_(on) represents the values of one feature variablewhile each column represents the feature vector of a training pattern.Similarly, the feature vectors corresponding to all of the off-rampmaneuvers form the training matrix X_(off)=[x_(1off) x_(2off) x_(Loff)].The training matrix X_(on) is used for the design of the styleclassification based on on-ramp maneuvers while the training matrixX_(off) is for the design based on the off-ramp maneuvers. Because thedesign process is the same for both maneuvers, X=[x₁ x₂ . . . x_(L)] isused to represent the training matrix.

For the design of the LDA-based feature extraction, the goal is to trainthe linear data projection Y=U^(T)X such that the ratio of thebetween-class variance to the within-class variance is maximized, whereX is an N-by-L training matrix, i.e., X_(on) for the on-ramp maneuverand X_(off) for the off-ramp maneuvers, and the transform matrix U isthe result of the training. Commercial or open-source algorithms thatcompute the matrix U are available and well-known to those skilled inthe art. The inputs to those algorithms include the training matrix Xand the corresponding class labels. In one embodiment, the class labelscan be 1-5 with 1 indicating a conservative driver, 3 indicating atypical driver and 5 being a sporty driver. In addition, a class label 0can be added to represent those hard-to-decide patterns. The classlabels are determined based on expert opinions by observing the testdata. The outputs of the LDA algorithms include the matrix U and the newfeature matrix Y.

The feature selection is conducted on the feature matrix Y. In oneembodiment, an Exhaustive Search is used to evaluate the classificationperformance of each possibly combination of the extracted features. Thenew features still consist of n features, and there are Σ_(i−1) ^(n)C^(i) _(n) possible combinations of the n features. The ExhaustiveSearch evaluates the classification performance of each possiblecombination by designing an SVM based on the combination and derivingthe corresponding classification error. The combination that yields thesmallest classification error is regarded as the best combination wherethe corresponding features {i₁ i₂ . . . i_(m)} determine the matrix[u_(i1) u_(i2) . . . u_(im)]. Conveniently, the SVM corresponding to thebest feature combination is the SVM classifier. Since commercial oropen-source algorithms for SVM designs are well-known to those skilledin the art, a detailed discussion is not necessary herein.

It is noted that although SVM is used as the classification technique,the present invention can easily employ other techniques, such as fuzzylogic, clustering or simple threshold-based logics. Similarly, otherfeature extraction and feature selection techniques can be easilyemployed in lieu of the LDA and Exhaustive Search.

According to another embodiment of the present invention, the maneuveridentification processor 46 identifies a vehicle launching maneuver,which is the maneuver where a vehicle starts from a near-zero speed.Reliable indicators of vehicle launching maneuvers include an increasingvehicle speed and a persistently positive longitudinal acceleration.Therefore, measurements of vehicle speed and/or vehicle longitudinalacceleration can be used to detect or identify a vehicle launchingmaneuver. If vehicle longitudinal acceleration is not directly measured,the acceleration can be computed by differentiating vehicle speedmeasurements. The maneuver identification processor 46 is only activatedto detect a vehicle launching maneuver when the gear is shifted todrive.

FIG. 22 is a flow chart diagram 510 showing a process for identifying avehicle launching maneuver, according to an embodiment of the presentinvention. To keep the integrity of the data associated with anidentified maneuver, the system keeps recording and refreshing at acertain period, such as T=2 s, of data.

The maneuver identifying algorithm begins by reading the filteredvehicle speed signal v_(x) and the vehicle longitudinal accelerationsignal a_(x) from a longitudinal accelerometer or by differentiatingvehicle speed measurements at box 512. The maneuver identifyingalgorithm then proceeds according to its operational states denoted bythe Boolean variable Start_flag and End_flag, where Start_flag isinitialized to zero and End_flag is initialized to one. The algorithmthen determines whether Start_flag is zero at block 514 to determinewhether the vehicle is in a vehicle launching maneuver. If Start_flag izero, then the vehicle 10 is not in a vehicle launching maneuver.

The algorithm then determines if the vehicle has started a vehiclelaunching maneuver by determining whether the conditions of decisiondiamond 516 have been met, namely, v_(x)(t−t₁−Δt)<v_(th),v_(x)(t−t₁:t)≧v_(th) and mean(a_(x)(t−t₁:t))≧a_(th1). In onenon-limiting embodiment, t₁ is a time window of about 1 s, Δt is thesampling time of the speed measurements, and v_(th) and a_(th1) arepredetermined thresholds, such as v_(th)=2 m/s and a_(th1)=0.05 m/s². Ifall of the conditions of the decision diamond 516 have been met, thenthe vehicle 10 has started launching, so the algorithm sets Start_flagto one and End_flag to zero at box 518. The algorithm then determines astarting time t_(start) at box 520, and proceeds to collect further dataat box 528. If the conditions of the decision diamond 516 are not met,the vehicle 10 is not in a launching maneuver, and the process goes tothe box 528 for collecting data.

If the Start_flag is not zero at the block 514 where the vehicle 10 hasbeen identified to be in a vehicle launching maneuver, the algorithmdetermines whether the vehicle launching maneuver has been completed bydetermining whether the longitudinal acceleration is within a smallthreshold, such as a_(th2)=0.02 m/s² during the last time t₁ s. Todetermine this, the algorithm determines whethermean(a_(x)(t−t₁:t))<a_(th2) at decision diamond 522. If this conditionis met at the decision diamond 522, then the vehicle launching maneuverhas been completed, and the algorithm sets Start_flag equal to zero andEnd_flag equal to one at box 524, and sets the time t_(end)=t−t₁ at box526. If the condition of the decision diamond 522 has not been met, thevehicle 10 is still in the vehicle launching maneuver, so the algorithmproceeds to the block 528 to collect more data. As the maneuveralgorithm determines the beginning and the end of the vehicle launchingmaneuver, the data selection processor 48 stores a corresponding datasegment based on Start_flag, End_flag, t_(start) and t_(end).

FIG. 23 is a flow chart diagram 530 showing a process used by the dataselection processor 48 for storing the data corresponding to aparticular vehicle launching maneuver. The flow chart diagram 530 issimilar to the flow chart diagram 130 discussed above, where like stepsare identified by the same reference numeral. In this embodiment for thevehicle launching maneuver, if the End_flag is one at the block 142because the vehicle launching maneuver has been completed, and thevariable old_Start_flag is set to zero at the box 144, the algorithmdetermines whether the launching maneuver was a straight-line launchingmaneuver or a launching maneuver accompanied by a relatively sharp turnat decision diamond 532. In one embodiment, the algorithm determines ifthe launching maneuver is also a left or right turn based on the yawrate signal ω and its integration φ=∫_(t) _(start) ^(t) ^(end) ω(t)dt.If max(ω(t_(start):t_(end)))<ω_(th) or φ<φ_(th), where φ_(th) is apredetermined threshold, such as 60°, the maneuver is regarded as astraight-line launching maneuver, and the maneuver identifier valueM_(id) is set to one at box 534. If these conditions have not been metat the decision diamond 532, the vehicle 10 is traveling around arelatively sharp turn during the launching maneuver, where the maneuveridentifier value M_(id) is set to two at box 536. The algorithm thenoutputs the recorded data at box 538 including the maneuver identifiervalue M_(id), M_(seq)=M_(seq+1) and data_ready=1. The algorithm ends atbox 540.

In general, the sportier a driver is, the larger the throttle input andthe faster the vehicle accelerates during vehicle launching. Therefore,vehicle speed, longitudinal accelerating and throttle percentage shouldbe able to reveal a driver's driving style. Acceleration pedal force orposition can also be included if available. The collected data is,however, not suitable to be used directly for the classification becauseof the following two reasons. First, the collected data consists of thetime trace of the signals, which usually results in a fair amount ofdata. For example, a typical launching maneuver generally lasts morethan 5 seconds. Therefore, with a 10 Hz sampling rate, more than 50sample of each signal would be recorded for a typical vehicle launchingmaneuver. Data reduction is necessary to keep the classificationefficient. Second, the complete time trace of those signals is usuallynot effective for the classification. In fact, a critical design issuein classification problems is to derive discriminative features thatbest represent individual classes. As a result, the style classificationprocessor 52 includes a feature processor and a style classifier, asdiscussed above.

The following original discriminant features are chosen based onengineering insights, and include vehicle final speed at the end of thevehicle launching, the average acceleration, and an array of throttleindexes I_(throttle)=[I₁ . . . I_(i) . . . I_(N)] based on thedistribution of the throttle opening a. Each throttle index I_(i) isdefined as the percentage of the time when the throttle opening a isgreater than a threshold a_(thi). That is, if the launching maneuvertakes T_(total) seconds and during the period of time, the throttleopening a is greater than a_(thi)(0<a_(thi)<100%) for T_(i) seconds,then the throttle index I_(t)=T_(i)/T_(total). Examples of thethresholds [a_(th1) . . . a_(thi) . . . a_(thN)] can be [20% 30% 40% 50%60%] or from 10% to 90% with a 10% interval in between. Alternatively,time T_(total) can be defined as the time when a>a_(th) and T_(i) isdefined with a_(thi)>a_(th).

These original features are input to the feature extraction andsubsequently feature selection processors. In one embodiment, featureextraction and feature selection processes are removed for simplicity.The style classification processor 52 then classifies a driver's drivingstyle directly based on those original discriminants. Classificationtechniques, such as fuzzy logic, clustering, neural networks,self-organizing map and threshold-based logic can be used for the styleclassification.

A neural network based classifier 550 suitable for this purpose is shownin FIG. 24. The neural network classifier 550 includes an input layer552 having seven input neurons 554 corresponding to the sevendiscriminants, namely, vehicle final speed, average accelerate and a5-dimension throttle index array. The neural network classifier 550 alsoincludes a hidden layer 556 including neurons 558, and an output layer562 including three neurons 564, one for a conservative driver, one fora typical driver and one for a sporty driver, where branches 560 connectthe neurons 554 and 558. Alternatively, the output layer 562 of theneural network classifier 550 may have five neurons, each correspondingto one of the five levels ranging from conservative to sporty. Thedesign and training of a neural network classifier 550 is based onvehicle test data with a number of drivers driving under various trafficand road conditions.

The embodiment discussed above provides launching maneuvers for bothstraight-line launching and launching and turning withoutdifferentiating between the two. Alternatively, classifiers can bedesigned specifically for these two type of maneuvers, and discriminantsderived from the vehicle yaw rate and lateral acceleration can beincluded for the classification based on launching and turningmaneuvers.

According to another embodiment of the invention, the decision fusion inthe decision fusion processor 56 can be divided into three levels,namely a level-1 combination, a level-2 combination and a level-3combination. The level-1 combination combines the classification resultsfrom different classifiers that classify different maneuvers based on asingle maneuver, and is not necessary for maneuvers that have only onecorresponding classifier. The level-2 combination combines theclassification results based on multiple maneuvers that are of the sametype. For example, combining the classification results of the mostrecent curve-handling maneuver with those of previous curve-handlingmaneuvers. The level-3 combination combines the classification resultsbased on different types of maneuvers, particularly, combines theresults from the individual level-2 combiners. The level-2 combinationand the level-3 combination can be integrated into a single step, or canbe separate steps. The level-1 combination resides in the stylecharacterization processor 52 and the level-2 combination and thelevel-3 combination are provided in the decision fusion processor 56.

FIG. 25 is a block diagram of a style characterization processor 430that can be used as the style characterization processor 52, andincludes the level-1 combination. The information from the maneuveridentification processor 46, the data selection processor 48 and thetraffic/road condition recognition processor 50 are provided to aplurality of channels 432 in the processor 430, where each channel 432is an independent classification for the same specific maneuver. In eachchannel 432, original features of the maneuver are identified in anoriginal features processor 434, features are extracted in a featuresextraction processor 436, the features are selected in a featureselection processor 438 and the selected features are classified in aclassier 440. A level-1 combination processor 442 combines all of thestyles for different maneuvers and outputs a single styleclassification. For example, assume two classification channels aredesigned for the curve-handling maneuvers. Once a new curve-handlingmaneuver is identified and the data associated with this specificmaneuver is collected, the data is input to both channels at the sametime and each channel outputs a style classification result. Thelevel-one combination then combines the two results and outputs a singlestyle classification.

The level-1 combination is a standard classifier combination problemthat can be solved by various classifier combination techniques, such asvoting, sum, mean, median, product, max/min, fuzzy integral,Dempster-Shafter, mixture of local experts (MLE), neural networks, etc.One criterion for selecting combination techniques is based on theoutput type of the classifiers 440. Typically, there are three type ofclassifier outputs, namely, confidence, rank and abstract. At theconfidence level, the classifier outputs a numerical value for eachclass indicating their belief of probability that the given inputpattern belongs to that class. At the rank level, the classifier assignsa rank to each class with the highest rank being the first choice. Atthe abstract level, the classifier only outputs the class label as aresult. Combination techniques, such as fuzzy integral, MLEs and neuralnetworks require outputs at the confidence level, while voting andassociative switch only requires abstract-level outputs. In oneembodiment, the level-1 combination of the invention is based onmajority voting and Dempster-Shafter techniques.

Majority voting is one of the most popular decision fusion methods. Itassumes all votes, i.e., classification results from differentclassifiers, are equally accurate. The majority-voting based combinercalculates and compares the number of votes for each class and the classthat has the largest number of votes becomes the combined decision. Forexample, assume the classes of the driving style are labeled as i=1, 2,. . . , k, with a larger number representing a more aggressive drivingstyle. In addition, a class “0” is added to represent the hard-to-decidepatterns. The number of votes V_(i) for each class i=0, 1 . . . , k is:

$\begin{matrix}{{V_{i} = {\sum\limits_{j = 1}^{N}v_{ij}}},{{{with}\mspace{14mu} v_{ij}} = \{ \begin{matrix}{1,} & {{{if}\mspace{14mu} c_{j}} = i} \\{0,} & {{{if}\mspace{14mu} c_{j}} \neq i}\end{matrix} }} & (37)\end{matrix}$Where c_(j) is the output from classifier j and N is the total number ofclassifiers.

The combined decision is c=arg_(i=0, 1, . . . k) ^(max) V_(i). Inaddition, the combiner may also generate a confidential level based onthe normalized votes,

${{{conf}(i)} = \frac{V_{i}}{\sum\limits_{i = 0}^{K}V_{i}}},$and provides a confidence vector [conf(0) conf(1) conf(K)]^(T).

Alternatively, weighted voting can be used to combine abstract-leveloutputs as:V_(i)=Σ_(j=1) ^(N)∝_(ij)v_(ij)  (38)Where the weightings a_(ij) represent the correct rate of classifier jin classifying patterns belonging to class i. These weights can bepre-determined based on the test performance (generalizationperformance) of the corresponding classifiers. Deriving the correct ratefrom the test performance is well-known to those skilled in the art.

If the classifiers provide outputs at the confidence level, theDempster-Shafter method can be used to design the combiner. The detailsof the Dempster-Shafter theory and algorithms are well-known to thoseskilled in the art. Given the class labels as i=0, 1, . . . , k, eachclassifier outputs an K-by-1 vector [b_(j)(0) b_(j)(1) . . .b_(j)(K)]^(T), where b_(j)(i) is the confidence (i.e., the belief)classifier j has in that the input pattern belongs to class i. Theconfidence values should satisfy 0≦b_(j)(i)≦1 and Σ_(i=0)^(K)b_(j)(i)=1.

Applying the Dempster-Shafter theory to the level-1 combiner results inthe following combination rule:

$\begin{matrix}{{{{{conf}(i)} = \frac{{bel}(i)}{\sum\limits_{i = 0}^{K}{{bel}(i)}}},{{{with}\mspace{14mu}{{bel}(i)}} = {\sum\limits_{j = 1}^{N}{b_{j}(i)}}}}( \prod\limits_{{m = 1},\;{\ldots\mspace{11mu} N},\;{m \neq {j\mspace{11mu}{b_{m}{(0)}}}}}^{\;} )} & (39)\end{matrix}$

As a result, the combiner also outputs a K-by-1 vector [conf(0) conf(1). . . conf(k)]^(T), where conf(i) is the confidence in that the patternbelongs to class i. Similarly, conf(i) satisfy 0≦conf(i)≦1 and Σ_(i=0)^(K)conf(i)=1. The output of the combiner is treated as theclassification results based on a single maneuver, which is to becombined with results based on previous maneuvers of the same type inthe level-2 combination.

The results stored in the trip-logger 54 can be used to enhance theaccuracy and robustness of the characterization. To fulfill this task,the decision fusion processor 56 is incorporated. Whenever a newclassification result is available, the decision fusion processor 56integrates the new result with previous results in the trip-logger 54 bythe level-2 and level-3 combinations.

Different from the level-1 combination, where the pattern, i.e., anysingle maneuver, to be classified by different classifiers is the samepattern, the level-2 and the level-3 combinations deal with the issue ofcombining classification results corresponding to different patterns,i.e., multiple maneuvers of the same or different types. Strictlyspeaking, the level-1 combination is a standard classifier combinationproblem while the level-2 and the level-3 combinations are not. However,if a drivers driving style is regarded as one pattern, theclassification based on different maneuvers can be regarded as theclassification of the same pattern with different classifiers usingdifferent features. Consequently, classifier combination techniques canstill be applied. On the other hand, the different maneuvers can betreated as different observations at different time instances and thecombination problem can be treated with data fusion techniques. Todemonstrate how this works, the present invention shows one example foreach of the two approaches, namely, a simple weight-average baseddecision fusion that ignores the maneuver type and time differences, anda Bayes-based level-2 and level-3 combinations that take thosedifferences into consideration.

FIG. 26 is a block diagram of a decision fusion processor 450 that canbe the decision fusion processor 56 that receives the style profile fromthe trip-logger 54. The style classification result for the most recentmaneuver with M_(id)=i is stored in the style trip-logger 54. Based onthe maneuver identifier value M_(id), the style profile trip-logger 54outputs all of the results of the maneuvers identified as M_(id)=1 forthe level-2 combination and previous fused style result from maneuversof other types, where M_(id)≈i A switch 452 selects a particular level-2combination processor 545 depending on the type of the particularmaneuver. An output processor 456 selects the level-2 combination fromthe particular channel and outputs it to a level-3 combination processor 458.

Since the Level-2 combination combines the classification results basedon maneuvers of the same type, each type of maneuver that is used forstyle characterization should have its corresponding level-2 combiner.From the perspective of data fusion, a level-2 combination can beregarded as single sensor tracking, also known as filtering, whichinvolves combining successive measurements or fusing of data from asingle sensor over time as opposed to a sensor set. The level-2combination problem is to find the driving style x_(n) ^(m) based on theclassification results of a series of maneuvers that are of the sametype: Y_(n) ^(m)={y₁ ^(m) y₂ ^(m) . . . y_(n) ^(m)}, where m representsthe maneuver type and is the class label observed by the classifier (orthe level-1 combiner if multiple classifiers are used) based on the ithmaneuver of the maneuver type m.

Based on Bayes' theorem:

$\begin{matrix}{{P( x_{n}^{m} \middle| Y_{n}^{m} )} = {{P( { x_{n}^{m} \middle| y_{n}^{m} ,Y_{n - 1}^{m}} )} = \frac{{P( { y_{n}^{m} \middle| x_{n}^{m} ,Y_{n - 1}^{m}} )}{P( x_{n}^{m} \middle| Y_{n - 1}^{m} )}}{P( y_{n}^{m} \middle| Y_{n - 1}^{m} )}}} & (40)\end{matrix}$Where P represents the probability of the event.

Further assuming that:

1. The classification results are independent of each other, i.e.,P(y_(n) ^(m)|x_(n) ^(m), Y_(n−1) ^(m))=P(y_(n) ^(m)|x_(n) ^(m)), and

2. The driving style x_(n) ^(m) obeys a Markov evolution, i.e., P(x_(n)^(m)|Y_(n−1) ^(m))=Σ_(x) _(n−1) ^(m) ₌₀ ^(K)P(x_(n) ^(m)|x_(n−1) ^(m),Y_(n−1) ^(m))P(x_(n−1) ^(m)|Y_(n−1) ^(m))=Σ_(x) _(n−) ^(m) ⁻⁰^(K)P(x_(n) ^(m)|x_(n−) ^(m))P(x_(n−1) ^(m)|Y_(n−1) ^(m)),

Accordingly, P(x_(n) ^(m)|Y_(n) ^(m)) can be simplified as:

$\begin{matrix}\begin{matrix}{{P( x_{n}^{m} \middle| Y_{n}^{m} )} = {P( { x_{n}^{m} \middle| y_{n}^{m} ,Y_{n - 1}^{m}} )}} \\{= \frac{{P( y_{n}^{m} \middle| x_{n}^{m} )}( {\sum\limits_{x_{n - 1}^{m} = 0}^{K}{{P( x_{n}^{m} \middle| x_{n - 1}^{m} )}{P( x_{n - 1}^{m} \middle| Y_{n - 1}^{m} )}}} )}{P( y_{n}^{m} \middle| Y_{n - 1}^{m} )}}\end{matrix} & (41)\end{matrix}$

In equation (41), P(y_(n) ^(m)|x_(n) ^(m)) represents the probability ofobserving a class y_(n) ^(m) given the hypothesis that the maneuver isactually a class x_(n) ^(m) maneuver. Since P(x_(n) ^(m)=i) (with i=0,1, . . . K) is usually unknown, equal probability is usually assumed:P(x_(n) ^(m)=i)=1/(K+1). Consequently, P(y_(n) ^(m)|x_(n) ^(m))∝ P(x_(n)^(m), y_(n) ^(m))=P(y_(n) ^(m)=x_(n) ^(m)), where conf(x_(n) ^(m)) isthe confidence level provided by the classifier (or the level-1combiner).

P(x_(n) ^(m)|x_(n−1) ^(m)) in equation (41) represents the probabilityof a class x_(n) ^(m) maneuver following a class x_(n−1) ^(m) maneuver.

In an ideal driving environment, a driver's driving style would berather consistent as:

$\begin{matrix}{{P( x_{n}^{m} \middle| x_{n - 1}^{m} )} = \{ \begin{matrix}{1,} & {{{if}\mspace{14mu} x_{n}^{m}} = x_{n - 1}^{m}} \\{0,} & {{{if}\mspace{14mu} x_{n}^{m}} \neq x_{n - 1}^{m}}\end{matrix} } & (42)\end{matrix}$

However, factors such as traffic/road conditions, fatigue, andinattention may cause a driver to deviate from his/her “normal” drivingstyle. Such factors can be incorporated into P(x_(n) ^(m)|x_(n−1) ^(m))as:P(x _(n) ^(m) |x _(n−1) ^(m))=f(x _(n) ^(m) , x _(n−1) ^(m),Traffic_(index)(n), Road_(index)(n), driver_(state)(n))  (43)

If traffic/road conditions have already been considered in theclassification, P(x_(n) ^(m)|x_(n−1) ^(m)) can be simplified as:

$\begin{matrix}{{P( x_{n}^{m} \middle| x_{n - 1}^{m} )} = \{ \begin{matrix}{{1 - ɛ},{{{if}\mspace{14mu} x_{n}^{m}} \in \lbrack {{\max( {0,{x_{n - 1}^{m} - \beta}} )},{\min( {{x_{n - 1}^{m} + \beta},K} )}} \rbrack}} \\{ɛ,{{{if}\mspace{14mu} x_{n}^{m}} \notin \lbrack {{\max( {0,{x_{n - 1}^{m} - \beta}} )},{\min( {{x_{n - 1}^{m} + \beta},K} )}} \rbrack}}\end{matrix} } & (44)\end{matrix}$Where 0≦ε≦0.5 and 0≦β≦K (e.g., β=1).

P(x_(n−1) ^(m)|Y_(n−1) ^(m)) in equation (42) is the previouscombination results. The initial condition P(x₀ ^(m)|Y₀ ^(m)) can be setto be 1/K+1), i.e. equal for any of the classes ({0, 1, 2, . . . , K}).P(y_(n) ^(m)|Y_(n−1) ^(m)) in the denominator is for normalization suchthat Σ_(x) _(n) _(m) ₌₀ ^(K)P(x_(n) ^(m)|Y_(n) ^(m))=1.

In summary, the Bayes-based level-2 combination is executed as follows:

1. Initialization:

${{P( x_{0}^{m} \middle| Y_{0}^{m} )} = {{\frac{1}{K + 1}\mspace{14mu}{for}\mspace{14mu} x_{0}^{m}} = 0}},1,2,\ldots\mspace{11mu},{K;}$

2. Upon the classification of the nth maneuver of the maneuver type m,calculate P(x_(n) ^(m)|Y_(n−1) ^(m)) for x_(n) ^(m)=0, 1, 2, . . . , Kbased on equation (41);

3. Calculate the nominator in equation (42):(P(y _(n) ^(m) |x _(n) ^(m))P(x _(n) ^(m) |Y _(n−1) ^(m))) for x _(n)^(m)=0,1,2, . . . K;

4. Calculate P(y_(n) ^(m)|Y_(n−1) ^(m)):

${{P( y_{n}^{m} \middle| Y_{n - 1}^{m} )} = {\sum\limits_{x_{n}^{m} = 0}^{K}( {{P( y_{n}^{m} \middle| x_{n}^{m} )}{P( x_{n}^{m} \middle| Y_{n - 1}^{m} )}} )}};$and

5. Calculate the posterior probability

${{P( x_{n}^{m} \middle| Y_{n}^{m} )} = {{\frac{{P( y_{n}^{m} \middle| x_{n}^{m} )}{P( x_{n}^{m} \middle| Y_{n - 1}^{m} )}}{P( y_{n}^{m} \middle| Y_{n - 1}^{m} )}\mspace{14mu}{for}\mspace{14mu} x_{n}^{m}} = 0}},1,2,\ldots\mspace{11mu},{K.}$

The output of the level-2 combiner is a vector [P(0|Y_(n) ^(m))P(1|Y_(n) ^(mm)) P(2|Y_(n) ^(m)) . . . P(K|Y_(n) ^(m))]. The classcorresponding to the largest P(x_(n) ^(m)|Y_(n) ^(m)) is regarded as thecurrent driving style:

$\begin{matrix}{c_{n}^{m}\underset{{x_{n}^{m} = 0},1,\;{\ldots\mspace{11mu} K}}{\text{arg}\max}{P( x_{n}^{m} \middle| Y_{n}^{m} )}} & (45)\end{matrix}$

Similarly, Bayes' theorem can be applied to develop the level-3combiner. Upon the onset of a new maneuver, the level-2 combiner outputs[P(0|Y_(n) ^(m)) P(1|Y_(n) ^(m)) P(2|Y_(n) ^(m)) . . . P(K|Y_(n) ^(m))].The level-3 combiner then calculates P(x_(n)| Y _(n)), where Y_(n)={Y_(n) ¹ Y_(n) ² . . . Y_(n) ^(j) . . . Y_(n) ^(M)} with Y_(n)^(m)={y_(n) ^(m) Y_(n−1) ^(m)}, Y_(n) ^(j)={Y_(n−1) ^(j)} for j≠m, and Mis the number of maneuver types used for the classification.

Correspondingly, the rule to calculate P(x_(n)| Y _(n)) is:

$\begin{matrix}{{P( x_{n} \middle| {\overset{\_}{Y}}_{n} )} = {\frac{( {\prod\limits_{j = 1}^{M}{P( x_{n}^{j} \middle| Y_{n}^{j} )}} ){P( x_{n - 1} \middle| {\overset{\_}{Y}}_{n - 1} )}}{\prod\limits_{j = 1}^{M}{P( x_{n - 1}^{j} \middle| Y_{n - 1}^{j} )}} \times {normalization\_ scaler}}} & (46)\end{matrix}$

Where P(x_(n−1)| Y _(n−1)) is the previous results of the level-3combiner.

For j≠m, Y_(n) ^(j)=Y_(n−1) ^(j):P(x _(n) ^(j) |Y _(n) ^(j))=Σ_(n) _(n−1) _(j) ₌₀ ^(K) P(x _(n) ^(j) |x_(n−1) ^(j) , Y _(n) ^(j))P(x _(n−1) ^(j) |Y _(n) ^(j))=Σ_(x) _(n−1)_(j) ⁻⁰ P(x _(n−) ^(j))P(x _(n−1) ^(j) |Y _(n−1) ^(j)).  (47)Where P(x_(n−1) ^(j)|Y_(n−1) ^(j)) is based on the previous results fromeach individual level-2 Combiner and P(x_(n) ^(j)|x_(n−1) ^(j)) is basedon equation (43).

In summary, the level-3 combination can be executed as follows:

1. Update P(x_(n) ^(j)|Y_(n) ^(j)) based on equation (47) for j≠m, thatis, for all the maneuver types other than the type corresponding to thelatest maneuver, P(x_(n) ^(m)|Y_(n) ^(m)) is provided by the level-2combiner corresponding to maneuver type m.

2. Calculate

${B( x_{n} \middle| {\overset{\_}{Y}}_{n} )} = \frac{( {\prod\limits_{j = 1}^{M}{P( x_{n}^{j} \middle| Y_{n}^{j} )}} ){P( x_{n - 1} \middle| {\overset{\_}{Y}}_{n - 1} )}}{\prod\limits_{j = 1}^{M}{P( x_{n}^{j} \middle| Y_{n - 1}^{j} )}}$based on the previous results from individual level-2 combinersP(x_(n−1) ^(j)|Y_(n−1) ^(j)), and the previous result from the level-3combiner P(x_(n−1)| Y _(n−1));

3. Calculate the normalization scaler:

$\begin{matrix}{{normalization\_ scaler} = \frac{1}{\sum\limits_{x_{n} = 0}^{K}{B( x_{n} \middle| {\overset{\_}{Y}}_{n} )}}} & (48)\end{matrix}$

4. Calculate the posterior probability:P(x _(n) | Y _(n))=B(x _(n) | Y _(n))×normalization_scaler  (49)

The output of the level-3 combiner is also a vector [P(0| Y _(n)) P(1| Y_(n)) P(2| Y _(n)) . . . P(K| Y _(n))]. The class corresponding to thelargest P(x_(n)| Y _(n)) is regarded as the current driving style:

$\begin{matrix}{c_{n} = {\text{arg}{\max\limits_{x_{{n = 0},1,\;{\ldots\mspace{11mu} K}}}( x_{n} \middle| {\overset{\_}{Y}}_{n} )}}} & (50)\end{matrix}$

Bayes' theorem can also be used to design an integrated level-2 andlevel-3 combination by following steps similar to those described above.Therefore, the details of the design and implementation are not includedin this invention.

It is worth noting that though the combination disclosed in oneembodiment of the invention is based on Bayes' theorem, other classifiercombination and data fusion techniques, including voting, sum, mean,median, product, max/min, fuzzy integrals, Dempster-Shafter, Mixture ofLocal Experts (MLEs), and neural networks, can also be employed in lieuof Bayes' theorem.

The foregoing discussion discloses and describes merely exemplaryembodiments of the present invention. One skilled in the art willreadily recognize from such discussion and from the accompanyingdrawings and claims that various changes, modifications and variationscan be made therein without departing from the spirit and scope of theinvention as defined in the following claims.

1. A method for identifying whether a vehicle maneuver may be an on-rampor off-ramp maneuver, said method comprising: reading a vehicle speedsignal and a vehicle yaw rate signal from vehicle sensors; determiningwhether the vehicle is turning by determining whether the vehicle yawrate signal is greater than a first yaw rate threshold and, if so,determining that the vehicle has entered a curve that may be a curveportion of a highway on/off ramp; determining whether the vehicle hasexited the curve by determining whether the vehicle yaw rate signal isless than a second yaw rate threshold; determining whether thedifference between the vehicle speed at the beginning of the curve andat the end of the is less than a first vehicle speed threshold and, ifso, determining that the curve-handling maneuver is an off-rampmaneuver; determining whether the increase in vehicle speed during apredetermined time window is less than a second speed threshold;determining whether the vehicle speed during a predetermined time windowof the maneuver is greater than a third speed threshold; determiningwhether a difference of the vehicle speed during the time window minusthe speed at the start time is greater than a fourth speed threshold;and determining that the maneuver may be an on-ramp maneuver if theincrease in the vehicle speed becomes less than the second speedthreshold and the speed of the vehicle during the predetermined timewindow is greater than the third speed threshold and the difference inthe vehicle speed during the time window minus the speed of the vehicleat the start time is greater than the fourth speed threshold.
 2. Themethod according to claim 1 further comprising determining that themaneuver is not an off-ramp maneuver if the time the vehicle spends onthe curve is greater than a first time period.
 3. The method accordingto claim 1 further comprising determining that the off-ramp maneuver hasended if the vehicle speed is less than a fifth speed threshold.
 4. Themethod according to claim 1 further comprising determining that themaneuver is not an off-ramp maneuver if the vehicle speed is not reducedenough during the maneuver.
 5. The method according to claim 1 whereinthe first yaw rate threshold is about 2 degrees per second, the secondyaw rate threshold is about 1 degree per second, the first speedthreshold is about 25 mph, the second speed threshold is about 55 mph,and the fourth speed threshold is about 3 mph.
 6. The method accordingto claim 1 further comprising classifying the vehicle maneuver todetermine a driver's driving style if the maneuver is an on-ramp or anoff-ramp maneuver.
 7. The method according to claim 6 whereinclassifying the on-ramp or off-ramp maneuver to determine a driver'sdriving style includes using selected discriminant features derived orobtained from the maneuver.
 8. The method according to claim 7 whereinthe discriminant features are derived or obtained from the groupcomprising a maximum lateral acceleration, a maximum yaw rate, anaverage acceleration, a maximum throttle opening and an array ofthrottle indices for an on-ramp maneuver and a maximum lateralacceleration, a maximum yaw rate, an average deceleration, a maximumbrake pedal force and an array of braking indices for an off-rampmaneuver.
 9. The method according to claim 7 wherein obtaining thediscriminant features includes using a linear discriminant analysisprocess.
 10. The method according to claim 7 wherein obtaining thediscriminant features includes using a technique selected from the groupcomprising principal component analysis, linear discriminant analysis,kernel principal component analysis and generalized discriminantanalysis, and selecting the discriminant features includes using atechnique selected from the group comprising exhaustive search,branch-and-bound search, sequential forward/backward selection andsequential forward/backward floating search.
 11. The method according toclaim 6 wherein classifying the maneuver includes using a support vectormachine.
 12. The method according to claim 6 wherein classifying themaneuver includes using a technique selected from a group comprisingfuzzy logic, clustering, neural networks, support vector machines andthreshold-based logics.
 13. A method for identifying whether a vehiclemaneuver may be an on-ramp or off-ramp maneuver, said method comprising:reading a vehicle speed signal and a vehicle yaw rate signal in vehiclesensors; determining whether the vehicle is turning by determiningwhether the vehicle yaw rate signal is greater than a first yaw ratethreshold and, if so, determining that the vehicle has entered a curvethat may be a curve portion of a highway on/off ramp; determiningwhether the vehicle has exited the curve by determining whether thevehicle yaw rate signal is less than a second yaw rate threshold;determining whether the difference between the vehicle speed at thebeginning of the curve and at the end of the is less than a firstvehicle speed threshold and, if so, determining that the curve-handlingmaneuver is an off-ramp maneuver; determining whether the increase invehicle speed during a predetermined time window is less than a secondspeed threshold; determining whether the vehicle speed during apredetermined time window of the maneuver is greater than a third speedthreshold; determining whether a difference of the vehicle speed duringthe time window minus the speed at the start time is greater than afourth speed threshold; determining that the maneuver may be an on-rampmaneuver if the increase in the vehicle speed becomes less than thesecond speed threshold and the speed of the vehicle during thepredetermined time window is greater than a third speed threshold and adifference in the vehicle speed during the time window minus the speedof the vehicle at the start time is greater than the fourth speedthreshold; and classifying the vehicle maneuver to determine a driver'sdriving style if the maneuver is an on-ramp or an off-ramp maneuverusing selected discriminant features obtained or derived from themaneuver.
 14. The method according to claim 13 further comprisingdetermining that the off-ramp maneuver has ended if the vehicle speed isless than a fifth speed threshold.
 15. The method according to claim 13further comprising determining that the maneuver is not an off-rampmaneuver if the vehicle speed is not reduced enough during the maneuver.16. The method according to claim 13 wherein the first yaw ratethreshold is about 2 degrees per second, the second yaw rate thresholdis about 1 degree per second, the first speed threshold is about 25 mph,the second speed threshold is about 55 mph, and the fourth speedthreshold is about 3 mph.
 17. The method according to claim 13 whereinthe discriminant features are obtained or derived from the groupcomprising a maximum lateral acceleration, a maximum yaw rate, anaverage acceleration, a maximum throttle opening and an array ofthrottle indices for an on-ramp maneuver and a maximum lateralacceleration, a maximum yaw rate, an average deceleration, a maximumbrake pedal force and an array of braking indices for an off-rampmaneuver.
 18. The method according to claim 13 wherein obtaining thediscriminant features includes using a linear discriminant analysisprocess.
 19. The method according to claim 13 wherein classifying themaneuver to determine a driver's driving style includes using a supportvector machine.
 20. A system for identifying a vehicle maneuver as apossible on-ramp or off-ramp maneuver, said system comprising: vehiclesensors that provide a vehicle speed signal and a vehicle yaw ratesignal; means for determining whether the vehicle is turning bydetermining whether the vehicle yaw rate signal is greater than a firstthreshold and, if so, determining that the vehicle has entered a curvethat might be a curve portion of a highway on/off ramp; means fordetermining whether the vehicle has exited the curve by determiningwhether the vehicle yaw rate signal is less than a second yaw ratethreshold; means for determining whether the difference between vehiclespeed at the beginning of the curve and at the end of the curve is lessthan a first vehicle speed threshold and, if so, determining that thecurve-handling maneuver is an off-ramp maneuver; means for determiningwhether the increase in vehicle speed during a predetermined time windowis less than a second speed threshold; means for determining whether thevehicle speed during a predetermined time window of the maneuver isgreater than a third speed threshold; means for determining whether adifference of the vehicle speed during the time window minus the speedat the start time is greater than a fourth speed threshold; and meansfor determining that the maneuver may be an on-ramp maneuver if theincrease in the vehicle speed becomes less than the second speedthreshold and the speed of the vehicle during the predetermined timewindow is greater than the third speed threshold and the difference inthe vehicle speed during the time window minus the of the vehicle at thestart time speed is greater than the fourth speed threshold.
 21. Thesystem according to claim 20 further comprising means for determiningthat the maneuver is not an off-ramp maneuver if the time during thecurve-handling maneuver is greater than a first time period.
 22. Thesystem according to claim 20 further comprising means for determiningthat the off-ramp maneuver has ended if the vehicle speed is less than afifth speed threshold.
 23. The system according to claim 20 furthercomprising means for determining that the maneuver is not an off-rampmaneuver if the vehicle speed is not reduced enough during the maneuver.24. The system according to claim 20 wherein the first yaw ratethreshold is about 2 degrees per second, the second yaw rate thresholdis about 1 degree per second, the first speed threshold is about 25 mph,the second speed threshold is about 55 mph, and the fourth speedthreshold is about 3 mph.
 25. The system according to claim 20 furthercomprising means for classifying the vehicle maneuver to determine adriver's driving style if the maneuver is an on-ramp or an off-rampmaneuver.
 26. The system according to claim 25 wherein the means forclassifying the on-ramp or off-ramp maneuver includes means for usingselected discriminant features obtained or derived from the maneuver.27. The system according to claim 26 wherein the discriminant featuresare obtained or derived from the group comprising a maximum lateralacceleration, a maximum yaw rate, an average acceleration, a maximumthrottle opening and an array of throttle indices for an on-rampmaneuver and a maximum lateral acceleration, a maximum yaw rate, anaverage deceleration, a maximum brake pedal force and an array ofbraking indices for an off-ramp maneuver.
 28. The system according toclaim 26 wherein the means for obtaining or deriving the discriminantfeatures uses a linear discriminant analysis process.
 29. The systemaccording to claim 26 wherein the means for obtaining or deriving thediscriminant features uses a technique selected from the groupcomprising principal component analysis, linear discriminant analysis,kernel principal component analysis and generalized discriminantanalysis, and the means for selecting the discriminant features isselected from the group comprising exhaustive search, branch-and-boundsearch, sequential forward/backward selection and sequentialforward/backward floating search.
 30. The system according to claim 25wherein the means for classifying the maneuver to determine a driver'sdriving style includes using a support vector machine.